SURVEY OF TRAFFIC NOISE
REDUCTION PRODUCTS,
MATERIALS, AND
TECHNOLOGIES
Final Report 584
Prepared by:
Vi Brown
Prophecy Consulting Group, LLC
2005 S. Henkel Circle
Mesa, AZ 85202- 6564
December 2008
Prepared for:
Arizona Department of Transportation
206 South 17th Avenue
Phoenix, Arizona 85007
In cooperation with
U. S. Department of Transportation
Federal Highway Administration
The contents of the report reflect the views of the authors who are responsible for the facts and
the accuracy of the data presented herein. The contents do not necessarily reflect the official
views or policies of the Arizona Department of Transportation or the Federal Highway
Administration. This report does not constitute a standard, specification, or regulation. Trade or
manufacturers’ names which may appear herein are cited only because they are considered
essential to the objectives of the report. The U. S. Government and The State of Arizona do not
endorse products or manufacturers.
This report can also be found on our web site…
http:// www. dot. state. az. us/ ABOUT/ atrc/ Publications/ Publications. htm
Technical Report Documentation Page
1. Report No.
FHWA- AZ- 08- 584
2. Government Accession No.
3. Recipient's Catalog No.
4. Title and Subtitle
5. Report Date
December 2008
Survey of Traffic Noise Reduction Products, Materials, and
Technologies
6. Performing Organization Code
7. Author
Vi Brown
8. Performing Organization Report No.
9. Performing Organization Name and Address
10. Work Unit No.
Prophecy Consulting Group, LLC
2005 S. Henkel Circle
Mesa, AZ 85202- 6564
11. Contract or Grant No.
T0549A0028
12. Sponsoring Agency Name and Address
ARIZONA DEPARTMENT OF TRANSPORTATION
206 S. 17TH AVENUE
13. Type of Report & Period Covered
FINAL REPORT
April 2005 – February 2008
PHOENIX, ARIZONA 85007
Project Manager: Estomih M Kombe, PhD, PE
14. Sponsoring Agency Code
15. Supplementary Notes
Prepared in cooperation with the U. S. Department of Transportation, Federal Highway Administration
16. Abstract
Noise is one of the most pervasive forms of environmental pollution. It is everywhere and affects our lives at
home, work and play. By definition, noise is any unwanted or excessive sound. Highway traffic noise is a
major issue for transportation agencies. The objective of this study was to identify noise reduction products,
materials, and technologies currently available and that may have potential as noise mitigation alternatives.
The literature review and survey identified measures that are being used by U. S. transportation organizations
as well as international efforts. Some key findings from the literature review show the following best
practices:
- Pavement Noise Reduction Products – noise or sound walls dominate this category and have been used
for decades in the U. S. Findings from the literature revealed a variety of materials to choose from that are
both aesthetically attractive, and effective in reducing sound from tire pavement noise. The cost of installing
products will need to be evaluated on a case by case basis with the vendor or for each applicable product.
- Pavement Noise Reduction Materials – The operating speed of the roadway should be factored into the
roadway design for quiet pavements. European studies show that higher porous mixtures tend to clog under
slower speeds. Two layer- porous mixes have been found to be effective in Europe and the US. An
important attribute for consideration in two layer- porous mix design and placement is aggregate size.
- Pavement Noise Reduction Technologies - use of thin- textured surfacings with a negative pavement
depression are recommended for urban or low- speed roadway sections. Diamond grinding enhances noise
reduction on concrete surfaces in sensitive locations.
- Other Pavement Noise Reduction Measures – looking forward, transportation officials are encouraged to
develop an integrated approach to roadway noise reduction. Instead of relying on a single measure, the
recommended forward strategy is to develop the ability to model the effectiveness of a number of different
measures to achieve greater noise reduction.
17. Key Words
Noise Barriers, Noise Walls, Roadway Noise
Mitigation, Vehicle Noise, Highway Noise
Reduction
18. Distribution Statement
Document is available to the
U. S. public through the
National Technical Information
Service, Springfield, Virginia
22161
23. Registrant's Seal
19. Security Classification
Unclassified
20. Security Classification
Unclassified
21. No. of Pages
86
22. Price
SI* ( MODERN METRIC) CONVERSION FACTORS
APPROXIMATE CONVERSIONS TO SI UNITS APPROXIMATE CONVERSIONS FROM SI UNITS
Symbol When You Know Multiply By To Find Symbol Symbol When You Know Multiply By To Find Symbol
LENGTH LENGTH
in inches 25.4 millimeters mm mm millimeters 0.039 inches in
ft feet 0.305 meters m m meters 3.28 feet ft
yd yards 0.914 meters m m meters 1.09 yards yd
mi miles 1.61 kilometers km km kilometers 0.621 miles mi
AREA AREA
in2 square inches 645.2 square millimeters mm2 mm2 Square millimeters 0.0016 square inches in2
ft2 square feet 0.093 square meters m2 m2 Square meters 10.764 square feet ft2
yd2 square yards 0.836 square meters m2 m2 Square meters 1.195 square yards yd2
ac acres 0.405 hectares ha ha hectares 2.47 acres ac
mi2 square miles 2.59 square kilometers km2 km2 Square kilometers 0.386 square miles mi2
VOLUME VOLUME
fl oz fluid ounces 29.57 milliliters mL mL milliliters 0.034 fluid ounces fl oz
gal gallons 3.785 liters L L liters 0.264 gallons gal
ft3 cubic feet 0.028 cubic meters m3 m3 Cubic meters 35.315 cubic feet ft3
yd3 cubic yards 0.765 cubic meters m3 m3 Cubic meters 1.308 cubic yards yd3
NOTE: Volumes greater than 1000L shall be shown in m3.
MASS MASS
oz ounces 28.35 grams g g grams 0.035 ounces oz
lb pounds 0.454 kilograms kg kg kilograms 2.205 pounds lb
T short tons ( 2000lb) 0.907 megagrams
( or “ metric ton”)
mg
( or “ t”)
mg megagrams
( or “ metric ton”)
1.102 short tons ( 2000lb) T
TEMPERATURE ( exact) TEMPERATURE ( exact)
º F Fahrenheit
temperature
5( F- 32)/ 9
or ( F- 32)/ 1.8
Celsius temperature º C º C Celsius temperature 1.8C + 32 Fahrenheit
temperature
º F
ILLUMINATION ILLUMINATION
fc foot candles 10.76 lux lx lx lux 0.0929 foot- candles fc
fl foot- Lamberts 3.426 candela/ m2 cd/ m2 cd/ m2 candela/ m2 0.2919 foot- Lamberts fl
FORCE AND PRESSURE OR STRESS FORCE AND PRESSURE OR STRESS
lbf poundforce 4.45 newtons N N newtons 0.225 poundforce lbf
lbf/ in2 poundforce per
square inch
6.89 kilopascals kPa kPa kilopascals 0.145 poundforce per
square inch
lbf/ in2
SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380
v
Table of Contents
Page
Section 1 - Introduction ........................................................................................... 1
1.1 Scope of Work ....................................................................................... 1
1.2 Report Organization............................................................................... 3
Section 2 – Literature Review.................................................................................. 5
2.1 Noise Reduction Products...................................................................... 5
2.2 Noise Reduction Materials..................................................................... 8
2.3 Noise Reduction Technologies ............................................................ 15
2.4 Other Considerations for Noise Source Reduction.............................. 26
Section 3 – Noise Reduction Survey .................................................................... 29
3.1 Development of Questionnaire ............................................................ 29
3.2 List of Potential Respondents .............................................................. 30
3.3 Preliminary Noise Survey.................................................................... 30
3.4 Noise Reduction Survey ...................................................................... 31
Section 4 – Survey Results .................................................................................... 33
4.1 Overall Response Rate......................................................................... 33
4.2 Sample Validation................................................................................ 33
4.3 Survey Results ..................................................................................... 33
Section 5 – Potential Growth of Noise Reduction Measures................................. 35
5.1 Products................................................................................................ 35
5.2 Materials .............................................................................................. 36
5.3 Technologies........................................................................................ 37
5.4 Other Measures .................................................................................... 38
Section 6 – Conclusions and Recommendations ................................................... 39
List of References .................................................................................................. 41
Appendix 1 Selected Noise Reduction Survey Documents............................... 43
Appendix 2 Noise Reduction Survey Responses............................................... 51
Appendix 3 A Sampling of Traffic Noise Reduction Products ......................... 61
v
List of Tables
Title Page Number
Table 1 Total Noise Barrier Area by Material Type ( through 2004)............................ 7
Table 2 Noise Barrier Data for United States ( through 2004) ...................................... 7
Table 3 Noise From Different Pavement Surface Types ( International Studies) ......... 9
Table 4 Noise From Different Pavement Surface Types ( National Studies).............. 10
Table 5 Summary of Concrete Pavement Texture Options ........................................ 23
Table 6 Initial Noise Reduction Levels for Light Vehicles Road
to the Future Project....................................................................................... 25
Table 7 Noise Influencing Road Surface Parameters ................................................. 26
v
Glossary
Abbreviations
e- mail electronic mail
Symbols
ρ density
λ lambda ( wavelength)
μ micro
Units of Measurement
Sound
AC absorption coefficient
c speed of sound
CCA chromated copper arsenate
CNEL Community noise equivalent level
dB decibels
dBA decibels, A- weighted sound level
ITC Indoor Transmission Class
L level
Ldn Day- night noise level
Leq Equivalent noise level
Lmax Maximum noise level
Lx noise level exceeded by “ x” percent
NHDOT New Hampshire Department of Transportation
NRC Noise Reduction Coefficient
PSL pressure sound level
SEL single event level
STC Sound Transmission Class
STL Sound Transmission Loss
Other units of measurement
oC degree Celsius
oK degree Kelvin
cm centimeter
f frequency
ft feet
h hour
Hz hertz
in inch
kg kilogram
km kilometer
km/ h kilometer/ hour
LF linear feet
m meter
m2 square meter
m3 cubic meter
mi mile
mm millimeter
MPa 106 or 1 million Pascal
mph mile/ hour
N Newton
Pa Pascals
rms root mean square
s second
SF square feet
sq. yd. square yard
SQRT square root
P pressure
PLF pound per linear foot
pcf pound per cubic foot ( lbs/ ft3)
psi pound per square inch ( lbs/ in2)
psf pound per square feet ( lbs/ ft2)
W Watt
Acronyms
AASHTO American Association of State Highway and Transportation
Officials
ACPA American Concrete Paving Association
ADOT Arizona Department of Transportation
AMT Advanced Masonry Technology
ASI Acoustical Solutions, Inc.
ASTM American Society for Testing and Materials
ATRC Arizona Transportation Research Center
CPX close proximity
CRCP continuously reinforced concrete pavement
CSI Concrete Solutions, Inc.
DGAC dense graded asphalt concrete
DOT Department of Transportation
EAC exposed aggregate concrete
EPA Environmental Protection Agency
FHWA Federal Highway Association
FMCSA Federal Motor Carrier Safety Administration
HARMONOISE Harmonized, Accurate, and Reliable Prediction Methods for the
EU Directive on the Assessment and Management of
Environmental Noise
HITEC Highway Innovative Technology Evaluation Center
HMA hot mix asphalt
IPG Innovation Program ( Netherlands)
ISU Iowa State University
IST International Scanning Team
GVWR Gross Vehicle Weight Rating
KDOT Kansas DOT
MDOT Minnesota DOT
NCAT National Center for Asphaltic Technology
NCHRP National Cooperative Highway Research Program
NGOGFC new generation open graded asphalt friction course
OBSI on- board sound intensity
OGFC open graded asphalt friction course
OSHA Occupational Safety and Health Association
PERS porous elastic road surface
PIARC Permanent International Association of Road Congresses – the
previous name for the organization that is now known as the
World Road Association
PCC Portland cement concrete
PFC porous friction course
PWRI Public Works Research Institute ( Japan)
QPPP Quiet Pavement Pilot Program
QUASH ™ QUASH, a trademark of the Dow Chemical Company for a large
cell polyethylene foam product that is typically used for sound
absorption.
RFI reflective cracking interlayer
RFP request for proposal
SILVIA Silenda Via Project
SIRIUS Silent Roads for Urban and Extra- Urban Use ( European Union)
SMA stone matrix asphalt
SPL sound pressure level
TAC Technical Advisory Committee ( ADOT)
TLPA two layer porous asphalt
TxDOT Texas DOT
UK United Kingdom
UV ultra- violet
WIDOT Wisconsin DOT
1
Section 1
Introduction
Noise is one of the most pervasive forms of environmental pollution. It is everywhere and
affects our lives at home, work and play. By definition, noise is any unwanted or
excessive sound. It is an unwanted by- product of our modern way of life. While noise
emanates from many different sources, transportation noise is one of the most difficult
sources to avoid in society today. Highway traffic noise is a major contributor to
transportation noise.
Considering the impacts of traffic noise on members of the public, the Arizona
Department of Transportation ( ADOT), sought the services of a qualified firm or
individual to perform a survey of traffic noise reduction products, materials, and
technologies. Prophecy Consulting Group, LLC ( hereafter referred to as Project
Researcher) provided these services under Contract No. T0549A00028.
The Department provided the following objectives for the traffic noise reduction
study:
a. Identify noise reduction products, materials, and technologies currently available
and that have potential as noise mitigation alternatives.
b. Compile available performance information and discuss whether a full- scale
testing program by the department is recommended.
This report provides the results of this research study and recommends future work or
activities on this topic.
1.1 Scope of Work
A project approach was initially provided in the request for proposal ( RFP) document.
The Work Plan agreed upon by the Technical Advisory Committee ( TAC) and the
Project Researcher identified seven project tasks. :
Task 1: Develop Work Plan
A draft work plan was developed by the Project Researcher and distributed to members
of the TAC prior to a project meeting on March 18, 2005. Elements of the draft work
plan were discussed during this meeting.
The draft work plan was updated to include the recommended changes by the TAC
during the meeting and subsequent comments. The work plan was approved on April 5,
2005.
2
Task 2: Conduct Literature Review
A literature review was performed. Existing work in the field of noise reduction
products, materials, and technologies was reviewed. Research tools used included
technical journal indices and abstracts, other periodicals, newspapers, text books,
handbooks, directories, the internet, and technical societies.
The TAC recommended that the Project Researcher prioritize the research into three
areas of noise reduction approaches: Products, Technologies, and Materials. For each
relevant reference, the researcher was to document: the work that was done, the
organization that conducted the research, the date of the study, the research outcome or
findings, ease of implementation and associated costs.
Task 3: Survey Government and Non- government Organizations
Using the results of the literature review, a survey was developed and sent to government
and non- government agencies. To better meet the requirements of the task, a question on
the survey queried the organization on its expected future use of any noise reduction
product, material, and/ or technology.
The list of government and non- government agencies was developed by the Project
Researcher with input from the ADOT Project Manager. Contacted agencies were
encouraged to submit the survey by email.
Task 4: Assess Growth of Alternative Noise Reduction Products, Materials and
Technologies
An assessment of the expected growth in the acceptability and use of alternative noise
reduction products, materials, and technologies was made based on the findings in Tasks
2 and 3.
Task 5: Recommend Next Steps
Using the information obtained in Tasks 2 thru 4, the Project Researcher provided ADOT
with a list of recommended next steps for future work in the area of noise reduction
products, materials, and technologies. This list was developed by assessing available
performance data, scalability, and application of each proposed product, material or
technology. Arizona’s diverse climate, traffic, and roadway conditions were also
considered in the development of these recommendations.
Task 6: Submit Final Report
This document constitutes the Project Final Report. A separate four- page summary was
also prepared as a “ Research Note” for ADOT. The final report was prepared in
accordance with the ATRC document, “ Guidelines for Preparing ATRC Research
Reports, September 2003”.
3
Task 7: Make Oral Presentation to Research Council ( Optional)
If requested, the Project Researcher will make a presentation to ADOT’s Research
Council, or another group of stakeholders.
1.2 Report Organization
Section 1 – Introduction
Section 1 summarizes the scope of work for this research study, includes information on
noise control regulations at the federal, state, and local levels, and provides an outline of
the Project Final Report.
Section 2 – Literature Review
A summary of the literature on pavement noise reduction products, materials, and
technologies is provided in Section 2. The information and data presented is
representative of significant work that has or is being done in this area.
Section 3 – Survey Development
Section 3 provides information on the survey development and the process used to
identify and distribute it to potential respondents.
Section 4 – Survey Results
Results of the pavement noise reduction survey are summarized in Section 4.
Section 5 - Potential Growth of Pavement Noise Reduction Measures
Section 5 identifies those measures that are reasonably easy to implement and are most
likely to be used by ADOT and other transportation organizations in the near future based
on the findings of this research.
Section 6 – Conclusions and Recommendations
Conclusions of the research findings are provided in Section 6 along with
recommendations for future work or analysis on this topic.
A cross section of traffic noise reduction products identified in the literature survey is
provided in Appendix 3. No doubt this is not an exhaustive list but includes a wide array
of applications described in the literature.
4
5
Section 2
Literature Review
A review of the literature on pavement noise reducing products, materials, and
technologies was conducted to identify current and emerging methods and practices.
Findings from the literature review are reported by noise reduction category. The
references in this section highlight significant work done in the area.
2.1 Pavement Noise Reduction Products
For purposes of this study, a noise reduction product is considered an item that is readily
available on the market. The most commonly adopted noise reduction product that has
been used in the U. S. is noise walls. One of the attributes of a noise wall is that it has the
ability to reduce all noise coming from the roadway regardless of source.
Noise walls are built between the highway and the adjacent neighborhood. These
structures are expensive to build ( often $ 1 to $ 2 million per mile) and to maintain ( graffiti
is a major problem). In addition, sound waves can bend over and around objects, and
spread out with distance, therefore noise barriers may be limited in their usefulness to
distances of less than 400 m ( 436 yd) from the roadway. 1 Effective noise barriers can
reduce noise levels by 5 to 10 dB, cutting the loudness of traffic noise by as much as one
half. For example, a barrier that achieves a 10 dB reduction can reduce the sound level of
a typical tractor trailer pass- by to that of an automobile.
Barriers can be formed from earth mounds or " berms" along the road, from high vertical
walls, or from a combination of earth berms and walls. Earth berms have a very natural
appearance and are usually attractive. They also reduce noise by approximately 3 dB
more than vertical walls of the same height. However, earth berms can require large areas
of land to construct, especially if they are very tall. Walls require less space, but they are
usually limited to eight meters ( 25 feet) in height for structural and aesthetic reasons. 2
To effectively reduce the noise coming around its ends, a barrier should be at least eight
times as long as the distance from the home or receiver to the barrier. Noise barriers can
be constructed from earth, concrete, masonry, wood, metal, and other materials. To
effectively reduce sound transmission through the barrier, the material chosen must be
rigid and sufficiently dense ( at least 20 kg/ sq. m, or 36.9 lbs/ sq. ft). 3 All noise barrier
material types are equally effective, acoustically, if they have this density.
Two characteristics that distinguish one noise reduction product from another are the
Noise Reduction Coefficient ( NRC) and the Sound Transmission Class ( STC). 4 NRC is a
single- number index for rating how absorptive a particular material is. Although the
standard is often abused, it is simply the average of the mid- frequency sound absorption
coefficients ( 250, 500, 1000 and 2000 Hertz rounded to the nearest 5%). The NRC gives
6
no information as to how absorptive a material is in the low and high frequencies, nor
does it provide a relationship to the material’s barrier effect or STC.
STC is a single- number rating of the barrier effect of a material or assembly. Higher STC
values are more efficient for reducing sound transmission. For example, loud speech can
be understood fairly well through an STC 30 wall but should not be audible through an
STC 60 wall. The rating assesses the airborne sound transmission performance at a range
of frequencies from 125 to 4000 Hertz. This range is consistent with the frequency range
of speech. The STC rating does not assess low frequency sound transfer. Special
consideration must be given to spaces where the noise of concern is something other than
speech, such as mechanical equipment or music.
Even with a high STC rating, any penetration, air- gap, or “ flanking” path can seriously
degrade the isolation quality of a wall. Flanking paths are the means for sound to transfer
from one space to another other than through the wall. Sound can flank over, under, or
around a wall. Sound can also travel through common ductwork, plumbing or corridors.
There are no federal requirements specifying the materials to be used in the construction
of highway traffic noise barriers. 2 Individual State DOTs select the materials when
building these barriers. The selection is normally based in part on factors such as
aesthetics, durability, maintenance, cost, and the desires of the public.
2.1.1 Noise Wall Expenditure and Materials
For the year ending December 31, 2004, 45 State DOTs and the Commonwealth of
Puerto Rico constructed over 2,205 linear miles of sound barriers at a cost of over $ 3.4
billion in 2004 dollars. Five states ( Alabama, Mississippi, Montana, Rhode Island, and
South Dakota) and the District of Columbia did not construct noise barriers for the same
period. 3 Total noise barrier areas by material type are shown in Table 1, and a summary
of noise barrier data for the United States is provided in Table 2.
7
Table 1
Total Noise Barrier Area by Material Type ( through 2004) 3
Combination Barriers
Material
Square Feet
( Thousands)
Material Square Feet
( Thousands)
Concrete/ Precast 67,926 Wood/ Concrete 4,281
Block 33,993 Berm/ Wood 2,990
Concrete/ Unspecified 13,715 Concrete/ Block 2,154
Wood/ Post & Plank 5,912 Other 1,930
Berm Only 4,281 Berm/ Concrete 1,863
Metal/ Unspecified 4,279 Metal/ Concrete 1,786
Wood/ Glue Laminated 3,701 Berm/ Metal 1,439
Absorptive 3,629 Berm/ Block 795
Wood/ Unspecified 3,055 Concrete/ Brick 586
Other 1,812 Wood/ Metal 464
Brick 1,152 Berm/ Wood/ Concrete 348
Wood/ Block 283
Berm/ Wood/ Metal 171
Block/ Brick 8
Total 143,455 Total 19,098
Table 2
Noise Barrier Data for United States ( through 2004) 3
State
Square Feet ( Thousands)
State
Linear Miles
California 30,644 California 482.8
Virginia 11,227 Arizona 155.1
Arizona 11,226 Virginia 127.5
New Jersey 9,440 Ohio 112.4
Ohio 8,675 New Jersey 96.9
Maryland 8,422 Colorado 92.5
Minnesota 7,187 New York 90.7
New York 7,011 Pennsylvania 87.0
Florida 6,700 Minnesota 83.7
Pennsylvania 6,415 Maryland 81.8
10 State Total 106,946 1,410.4
Actual Cost ( Millions) 2004 Dollars Millions
California $ 399.6 California $ 592.8
Arizona 258.7 Arizona 284.6
New Jersey 202.4 New Jersey 277.5
Maryland 200.9 Maryland 253.6
Virginia 169.6 Virginia 225.3
New York 165.9 New York 207.3
Pennsylvania 159.6 Pennsylvania 197.8
Florida 150.7 Florida 175.9
Ohio 117.2 Ohio 139.0
Colorado 80.0 Minnesota 107.7
10 State Total $ 1,904.5 $ 2,461.4
Note: California did not supply barrier data for 1998- 2004.
8
2.1.2 Noise Wall Treatments and Coatings
Appendix 3 provides a sampling of traffic noise reduction products. While this is not an
exhaustive list, it does cover a wide array of potential applications found in the literature.
A recent concept in noise barrier design is the placement of sound absorptive materials on
top of barriers. Sound absorptive materials have been applied either on a large portion of
the surface area of the barrier, or at specific locations to reduce sound reflection off the
barrier surface. During the early 1970s, it was first proposed that lining the region in the
immediate vicinity of the edge of a barrier with sound absorptive material could result in
a potential reduction in sound pressure in the shadow zone. 5
Shadow zone is a term commonly used in oceanography or geology. Refraction produces
shadow zones that sound waves do not penetrate because of curvature. However, if the
object has a diameter greater than the acoustic wavelength, a “ sound shadow” is cast
behind the object where the sound is inaudible. ( Note: Some sound may be propagated
through the object depending on the material).
Acoustic treatments on the road side of barriers have been used to reduce the noise
reflected off the walls. The results of full scale experiments show that the performance of
a 2m ( 6.56ft) high barrier was reduced by 4 dBA when another reflective barrier of a
similar height was present on the other side of the road. 6 However, the researchers later
reported that the measured effects of applying absorptive materials to roadside barriers
are generally less than 1 dB on the A- weighted equivalent noise level, LAeq, and the A-weighted
noise level 10% of the time, LA10. Sound absorptive barrier tops or “ top
treatments” have been studied in theory as well as application with noise reductions
reported from 1 to 5 dBA. 6
The Institute for Safe, Quiet, and Durable Highways studied various shapes of sound
absorptive “ caps” and two alternative materials - glass fiber and polyolefin foam with
closed cells ( QUASH). This wall “ capping” concept was studied both in the laboratory
and on a section of sound barrier along US 20 in Elkhart County, Indiana. 7,8 Actual field
measurements showed that when the QUASH add- on device was attached to the existing
barrier edge, the benefit of the sound barrier increased between 2 dB and 5 dB at
frequencies from 2000 to 5000 Hz.
Although limited work has been done with barrier treatments, if an effective method
could be found, the possibility for greater noise reduction or deflection could be
significant in Arizona based on the amount of investment in noise barriers, and future
maintenance needs.
2.2 Noise Reduction Materials
The contribution to roadway noise created by tire- pavement interaction on the road
surface, pavement smoothness, and pavement texture is at issue here. In this subsection,
pavement noise reducing materials are defined as aggregate and other materials that are
9
applied to the surface as a part of the roadway design. As examples, these materials
include asphalt surfaces, portland cement concrete, sand and gravel.
Rubberized pavement, asphalt- rubber, and rubberized asphalt are often used
synonymously to describe a blend of asphalt cement, reclaimed tire rubber and certain
additives. The rubber component in this blend is at least 15% by weight of the total blend
and has reacted in the hot asphalt cement sufficiently to cause swelling of the rubber. 9
Interestingly, this non- proprietary, non- patented public process was developed in the
1960' s by a City of Phoenix engineer and has been routinely used in the U. S. by
transportation agencies in Arizona, California, Texas and Florida. The blend also has
been used on five continents. The higher binder content ( between 8 to 10%) allows for
more coating on the aggregate and produces a longer lasting pavement. Smoother ride
and noise reduction are two major benefits of asphalt- rubber hot mix pavements.
2.2.1 Pavement Treatments
The work done by European countries in using pavement surface type as a noise
reduction strategy has been well recognized and documented. Research by Kandhal10
shows that numerous studies were conducted in Europe in the 1980s and 1990s to
determine comparative noise levels of dense- grade hot mix asphalt ( HMA), open- graded
asphalt friction course ( OGFC), Portland cement concrete ( PCC) pavements, and stone
matrix asphalt ( SMA). The general conclusions drawn from these studies are provided in
Table 3.
Table 3: Noise From Different Pavement Surface Types ( International Studies) 10
Country/ Agency
( Year Reported)
Surface Type
Evaluated*
General Conclusions
British Columbia, Canada
( 1999)
HMA, OGFC After three years in service, the OGFC is quieter than the
HMA by 3.5 to 4.0 dBA.
Italy ( 1998) HMA, SMA As much as 7.0 dBA reduction in noise level has been reported
at 110 km/ h when SMA was compared to HMA
Germany ( 1991 and 1998) HMA, SMA SMA was 2.5 and 2.0 dBA quieter than HMA.
Nordic Countries ( 1994) HMA, OGFC A joint Nordic project determined OGFC to be quieter than
HMA by 3 to 5 dBA.
Belgium ( 1994) HMA, OGFC, PCC HMA was quieter than PCC ( old pavement) by 3.4 dBA,
OGFC was quieter than PCC by 7.5 dBA, OGFC was quieter
than transverse grooved PCC by 10.5 dBA.
World Road Association –
formerly PIARC ( 1993)
HMA, OGFC, PCC,
Chip Seal
The following ranges of noise levels have been reported in this
extensive report: OGFC 69- 77 dBA, HMA 72- 79.5 dBA, and
PCC 76- 85 dBA.
United Kingdom ( 1993) Rolled Asphalt,
OGFC, PCC
OGFC was quieter than rolled asphalt surface ( used in UK) by
4 decibels. OGFC was quieter than PCC by 6- 7 decibels.
Danish Road Institute
( 1992)
HMA, OGFC OGFC was quieter than HMA by 4 dBA.
Italy ( 1990) HMA, OGFC OGFC was quieter than HMA by 3 dBA
Germany ( 1990) HMA, OGFC OGFC was quieter than HMA by 4 to 5 dBA.
Sweden ( 1990) HMA, OGFC OGFC was quieter than HMA by 3.5 to 4.5 dBA.
France ( 1990) HMA, OGFC OGFC was quieter than HMA by 3 to 5 dBA.
Netherlands ( 1990) HMA, OGFC OGFC was quieter than HMA by about 3 dBA.
* HMA = dense- graded hot mix asphalt, OGFC = open- graded asphalt friction course, PCC = Portland cement concrete, SMA = stone matrix asphalt
1 0
Similarly, Khandal provides a summary of some noise level studies conducted in the U. S.
for pavement surfaces made of HMA, OGFC, PCC, and SMA in Table 4. Using dense-graded
HMA as the base reference, the average comparative noise levels for these
pavement surface materials are OGFC = - 4 dBA, SMA = - 2 dBA, HMA = 0 ( reference)
and PCC = + 3 dBA.
Table 4: Noise From Different Pavement Surface Types ( National Studies) 10
State Agency
( Year Reported)
Surface Type
Evaluated*
General Conclusions
Texas ( 2003) HMA, PCC An existing continuously reinforced concrete pavement ( CRCP) was
overlaid with asphalt- rubber OGFC. On average, the roadside noise
was reduced from 85 to 71 dBA. The reduction of 14 dBA is very
high and is possibly the largest noise reduction ever recorded on a
Texas DOT project.
California ( 2002) HMA, OGFC After four years in service on I- 80 near Davis, the OGFC is quieter
than the HMA by 4 to 6 dBA.
Michigan ( 2002) HMA, SMA, PCC A limited number of pavements were tested by close proximity
method. Considering the noise data obtained at 60 mph with an
aggressive tire pattern, the following noise levels were recorded in
dBA: SMA = 98.3, HMA = 98.9, and PCC = 98.9 to 100.8. For
PCC, the quietest surface was the diamond ground with 98.9 dBA,
which was about equal to HMA.
Michigan ( 2000,
2001)
HMA, OSMA,
PCC
The first study ( 2000) was conducted on I- 275, west of Detroit. It
indicated Superpave HMA was 4 to 5 dBA quieter than PCC. The
second study ( 2001) conducted on I- 94, west of Ann Arbor, showed
that a 12.5 mm SMA was approximately 4 dBA quieter than 12.5
mm Superpave HMA.
Wisconsin ( 1997) HMA, PCC The noise from HMA pavements was about 2 to 5 dBA less than
PCC pavements.
U. S. DOT ( 1995) HMA, OGFC, PCC Volpe National Transportation Center ( U. S. DOT) made numerous
noise measurements in multiple states to collect data for FHWA’s
noise model. For automobiles, PCC pavements were about 3 dBA
quieter than dense- graded HMA. OGFC was about 1.5 dBA quieter
than dense- graded HMA. ( Note: These OFGC data do not represent
European type new- generation OGFCs that are now used in the U. S.
and are significantly quieter.)
Minnesota ( 1995,
1987, and 1979)
HMA, OGFC, PCC OGFC was found to be quieter than HMA in the 1979 study. HMA
was found to be quieter than PCC in all three studies.
Oregon ( 1994) OGFC, PCC Compared to PCC pavements, the OGFC were 5.7 to 7.8 dBA
quieter.
Maryland ( 1994) HMA, SMA Average noise level of SMA was 1 dBA lower than HMA.
New Jersey ( 1994) HMA, SMA, PCC One PCC pavement and one HMA pavement were overlaid with
SMA. Noise levels were determined before and after the overlays.
Measurements during the afternoon rush hours showed SMA to be
quieter than PCC by 2.0 dBA before overlays.
Wisconsin ( 1993) HMA, SMA Similar to Maryland, the average noise level of SMA was 1 dBA
lower than HMA.
Maryland ( 1990) OGFC, PCC The OGFC was quieter by 2.3 to 3.6 dBA than the PCC pavement.
FHWA ( 1975) HMA, OGFC, PCC Noise level studies were conducted in Arizona, California, and
Nevada. Based on average dBA values, OGFC was quieter than
HMA by 2 dBA, and quieter than HMA by 2.1 dBA. The HMA
pavement was quieter than PCC by 2.0 dBA before overlays.
* HMA = dense- graded hot mix asphalt, OGFC = open- graded asphalt friction course, PCC = Portland cement concrete, SMA = stone
matrix asphalt
1 1
2.2.1.1 OGFC for Noise Reduction
The current rubberized asphalt that is being used in Europe and a few south- western
states is OGFC. 10 California DOT and Texas DOT ( TxDOT) have been actively involved
in quiet pavement studies utilizing OGFC. OGFC is referred to as porous friction course
( PFC) in Texas. TxDOT’s first PFC was placed in 1999. As of 2004, 25 additional PFC
projects had been completed. PFC mixtures have gained popularity as a paving material
due to their ability to reduce the risk of hydroplaning, reduce the amount of splash and
spray, reduce pavement noise, improve visibility of traffic striping in wet weather, and
improve ride quality. 11
Data reported in Table 4 for the State of California is the result of a three- year study to
determine if the noise attenuation benefits of OGFC decreased over time. A nine
kilometer ( 5.59 mile) portion of pavement on I- 80 near Davis, CA was repaved in June
1998. The new pavement cross section consisted of a 60 mm dense graded asphalt
concrete ( DGAC) leveling course that was overlaid with 25 mm ( 0.98 in) of OGFC.
Immediately after applying the DGAC base, roadside noise levels declined by 3 to 4 dBA
from baseline conditions. After application of the OGFC, roadside noise levels declined
by about 5 dBA from the baseline condition. Noise levels continued to be 4 to 6 dBA
lower than baseline condition over the entire study period. 11
Although OGFC provides a number of pavement noise reduction benefits, one of the
concerns reported at the SILVIA conference24 is that it is not porous, it is not pervious to
rainwater, and it does not perform well in colder climates. This is problematic for those
areas of Arizona at higher elevations and which experience colder winters than lower
elevation areas like metropolitan Phoenix and southern Arizona.
New generation OGFC ( NGOGFC) is also gaining popularity as a safe pavement,
especially for winter weather conditions. NGOGFC contains approximately 20 percent
more asphalt ( by volume) than conventional or first generation OGFC. NGOFC is
designed to have a minimum of 18 percent air voids. The design of conventional OGFC
did not focus on air voids. However, conventional OGFC mixtures typically contain
between 10 and 15 percent air voids. 11 At lower air voids percent levels moisture can get
trapped within the void matrix of the conventional OGFC. The void structure of
NGOGFC allows the mix to be more permeable and less likely to trap water.
A TxDOT report to their research management committee notes the following benefits of
NGOGFC:
• overall good friction and lower noise, in wet weather conditions - higher visibility
• reduced splash and spray
• reduced hydroplaning, and
• reduced night- time surface glare.
Also noted in the report are some of the common problems encountered with OGFC –
lack of durability ( raveling in 6 to 8 years), accumulation of frost and ice, and clogging of
pores. NGOGFC is also reported to be 22.5% more expensive than OGFC. 12
1 2
Transportation officials in The Netherlands have more than five years of experience with
second generation porous asphalt surface courses with rubberized asphalt binders,
ranging from test sections to large scale use. The new concept consists of a double-layered
porous asphalt construction, made up of a bottom layer of fine- graded porous
asphalt ( aggregate size 4 to 8 mm / 0.16 to 0.32in). The binder in both layers is
rubberized asphalt. The fine texture of the top layer causes a reduction of traffic noise,
from 3 to 4 dBA at 50 km/ h ( 31mph) up to 5.5 dBA at 100 km/ hr ( 62mph). 11
In 2005, the FHWA, American Association of State Highway Transportation Officials
( AASHTO), and the National Cooperative Research Highway Program ( NCRHP),
sponsored a scanning study of European quiet pavement systems. A cross- section team
of 14 state, federal, academic, and industry representatives visited five European
countries: Denmark, France, Italy, the Netherlands, and the United Kingdom ( UK). All
countries have policies that require the use of quiet pavement or other measures to reduce
traffic noise. Each country is also conducting research on quiet pavement technologies. 13
The focus of the tour was the three technologies below:
• Thin- surfaced, negatively textured gap- graded asphalt mixes ( e. g. Novachip,
micro- surfacing, and some SMA),
• Single- and double- layer highly porous asphalt mixes ( greater than 18% voids),
• Exposed aggregate concrete ( EAC) pavements.
The Danish government has experimented with both single- and double- layer porous
mixes and thin- layer mixes as pavement noise reducing strategies. The porous mixes
have the greatest potential to reduce noise by 3 to 5 dB, but have performance problems
with clogging and durability. Thin mixes are more cost- effective and appear to be more
durable. However, noise reduction achieved is lower at 1 to 3 dB. In some cases two-layer
OGFC or porous asphalt is being used as a noise- reducing strategy in place of
sound walls. Denmark requires porous mixtures to be at least 18 percent air voids. The
proposed system incorporates a large stone mix ( 16 or 22 mm / 0.62 or 0.86 in) in the
lower layer, and a smaller stone mix ( 5 or 8 mm / 0.20 or 0.31 in) in the upper layer. This
pavement system has added benefits in that it prevents the OGFC from clogging during
service. 10, 13
France employs the following techniques for pavement noise reduction: 13
• Use separate structural and surface characteristics,
• Use best- quality aggregates,
• Adjust pavement dressing to noise characteristics,
• Use smaller aggregate size for best adhesion ( skid resistance).
French transportation officials acknowledge the use of thicker surfacing ( 5 to 8 cm / 1.95
to 3.12 in) and continuous grading to ensure good waterproofing of the pavement.
However, very thin ( 2 to 3 cm / 0.78 to 1.17 in) and ultrathin ( 1.5 cm / 0.59 in) mixes
developed to improve the surface characteristics ( skid resistance, noise) are being used
today. The grading composition of mixes is 0 to 6 mm ( 0.23 in) and 0 to 10 mm ( 0.39 in)
gap graded. These surface mixes are usually 25 to 30 mm ( 0.98 to 1.17 in) thick with 5.7
1 3
to 5.9% asphalt. Gap grading appears to increase the raveling potential for these
pavements. The addition of 7 to 10% sand mortar has helped to resist raveling.
In the UK, plans are underway to resurface 60 % of the strategic road network with
quieter materials for a 10- year period ending in 2010.13 Transportation officials have
experimented with EAC finishes, but thin- layer quiet surfaces are now the paving
materials of choice because they are more cost effective, even on concrete pavements.
2.2.1.2 Concrete Treatment for Noise Reduction
Kansas DOT ( KDOT) rehabilitated eight miles of I- 435 with 3- inches of asphalt laid over
a 1- inch reflective cracking interlayer ( RCI). The interlayer was a polymer with a heavy
oil content – a modified emulsion as a tack coat between the two lifts. The finished HMA
overlay reduced the noise level from the original transverse tined PCC pavements by
about 7 dB. The National Center for Asphalt Technology ( NCAT) tested the pavement
surface for noise levels before and after the project. 14 Local residents described the noise
levels before and after the project as a “ difference between night and day”.
Similarly, Wisconsin DOT ( WIDOT) tested Italgrip, a very thin surface treatment
consisting of a two- part polymer resin, and found it to be a suitable and cost- effective
technique to enhance the safety and drainage characteristics of their roadways. The
Italgrip system is designed to improve the frictional characteristics of a pavement surface.
It is primarily intended for application in heavily trafficked short sections of roadway
with friction problems or high accident rates. 15 A 3 mm ( 0.12 in) Italgrip aggregate was
applied to both eastbound lanes, while a 4 mm ( 0.16 in) aggregate was applied to the
westbound lanes near I- 94.
The following steps were followed after diamond grinding of the roadway section:
• a two- part polymer adhesive was carefully applied to the pavement surface,
• the Italgrip aggregate was then back- spread over the polymer,
• after setting for a few hours, the surface was vacuum swept and re- opened to traffic.
The following outcomes were observed from the WIDOT study:
• grinding of the PCC pavement and application of the Italgrip resulted in no major
shift in frequency spectrum when comparing the tined PCC pavement, ground PCC
pavement and ground PCC pavement with Italgrip;
• a 3 dB decrease in the noise level due to diamond grinding, an additional 1 dB
reduction in noise level when the Italgrip is compared to the ground PCC pavement
at 96 km/ h and 104 km/ h ( 60 mph and 65 mph), and a 2 to 3 dB decrease in noise
level when the Italgrip is compared to the ground pavement between 1,550 and
2,000 Hz;
• a noticeable change in sound to the ear;
• no significant change in noise level at 112 km/ h ( 70 mph) between Italgrip and the
ground pavement;
• no significant noise level difference between the 3 mm and 4 mm ( 0.12 and 0.16
in) aggregate.
1 4
Prior to 1999, the Italgrip System had never been used in the United States. However, the
system had been in use in Italy for 10 years.
Although EAC pavements are commonly used in European countries, the technique has
not been routinely used in the United States. EAC pavements are normally constructed
using a two- layer “ wet on wet” paving process. The top layer thickness typically ranges
from 38 to 70 mm ( 1.5 to 2.75 in.). The mix contains fine siliceous sand and a high- qual-ity
coarse aggregate with an ideal maximum size of 6 to 12 mm ( 0.24 to 0.48 in.). Aggre-gates
used in the lower layer of the pavement can be of more modest durability and com-monly
include recycled materials that help reduce the overall cost of the concrete. Studies
have shown that the use of smaller aggregates provided better noise reduction levels. 16
The only large- scale EAC pavement project in the U. S. was completed in 1993 on
Interstate 75 in downtown Detroit, Michigan. The exposed aggregate concrete pavement
was comprised of a 254 mm ( 10 in.) jointed concrete pavement constructed in two lifts.
The top layer of the pavement was 64 mm ( 2.5 in.) thick with polish- resistant aggregates,
and the bottom layer was 191 mm ( 7.5 in.) thick with conventional aggregates. The lifts
were bound using a “ wet- on- wet” procedure. When compared to a conventional jointed
reinforced concrete pavement textured with transverse tines spaced 25 mm ( 1.0 in.) apart,
the section provided a reduction of only 0.4 dBA in exterior noise levels, although similar
European projects reported noise reductions between 4 and 5 dBA. 16
Researchers believe that the disappointing values may have resulted from too much
macrotexture on the exposed aggregate surface, combined with excessive spacing
between the coarse aggregate particles. This excessive spacing was a result of large sand
particles. Perhaps the difference in the U. S. and European experiences with EAC was a
motivating factor for the renewed interest in EAC pavements on the recent 2005 FHWA
scanning tour.
EAC pavements also exhibit properties associated with pavement texturing due to the
size of aggregates used and the texture depth of the stones. This material is also discussed
in Section 2.3, Pavement Noise Reduction Technologies.
Pervious or porous concrete is a material with large voids that are intentionally built into
the mix. The resulting permeability allows water ( and air) to flow readily through this
material. When used in highway applications, pervious concrete is typically used as a top
layer ( wearing course), providing both low noise emission and good drainage capacity.
The pervious concrete typically overlays a conventional ( dense) concrete pavement using
a “ wet- on- wet” process. Noise reduction in this composite system is a result of the
pervious material’s acoustical absorption, while strength and durability are improved by
the presence of the underlying concrete pavement layer. 16
Porosity levels for pervious concrete pavements typically range between 15% and 20%.
To attain good noise reduction characteristics, porosity should be at least 25%. Research
from Purdue University’s Institute of Safe, Quiet, and Durable Pavements has reported
that sound absorption levels were improved when higher porosity was used.
1 5
When pervious concrete pavement was first constructed in Belgium, it was found to
exhibit undesirable durability in freezing weather. Subsequently, polymer additives were
used along with higher cement content. The result was a significant improvement in the
service life. 13, 16 A policy that is currently being pursued in Japan is to replace all
pavements with pervious systems due to their safety and riding comfort. To change over
their existing concrete pavements to a pervious system, the preferred option is thin-bonded
pervious concrete overlays. 16 Laboratory simulation tests have demonstrated that
pervious concrete pavements can resist rutting and have a higher wear resistance to tire
chains than porous asphalt.
Since 1993, Japan’s Public Works Research Institute ( PWRI) has been developing a new
low- noise pavement that is referred to as “ Porous Elastic Road Surface” ( PERS).
Potential noise reduction levels in Equivalent Noise Level ( Leq) exceed 10 dBA. PWRI
has already solved several of the problems with PERS such as insufficient adhesion
between the pavement and the base course, low skid resistance, and poor fire resistance.
PERS was first constructed on Japan’s National Highway Route 46. However, noise
reduction levels measured in the field were less than expected due in part to the small size
of the construction area. The noise reduction levels measured at the site are lower than
those measured at the PWRI test facility. The noise reduction effect of PERS was found
in the 1/ 3- bandwidth frequency of 800 Hz and over. 17
In a separate study, pervious concrete pavements were evaluated in Japan with two
experimental concrete sections, 200 mm ( 7.9 in) in thickness. When compared to dense
asphalt pavements, they displayed noise reductions of 6 to 8 dBA for dry surfaces and 4
to 8 dBA for wet surfaces. This study was conducted with cars traveling at speeds from
40 to 75 km/ h ( 25 to 45 mph). For heavy trucks, noise reduction values were 4 to 8 dBA
and 2 to 3 dBA for dry and wet surfaces, respectively. 18
One disadvantage of using pervious concrete pavements is the clogging of the
pavement’s pores. The pores clog over time due to depositions in the voids of dirt and
dust from the road surroundings, from wear of the pavement itself, and from tires. 13, 16
2.3 Noise Reduction Technologies
For the purposes of this research study, a pavement noise technology may be a part of the
process, equipment, or machinery that is used to apply the paving material to the road
surface. It does not include paving materials.
2.3.1 Pavement Texturing
Pavement texturing can be designed and built into a pavement or placed upon hardened
concrete pavement by equipment. The National Concrete Pavement Technology Center at
Iowa State University ( ISU), FHWA, ACPA, and other organizations have partnered to
conduct a multi- part, seven- year Concrete Pavement Surface Characteristics Project. 16
Part 1, Task 2, of the ISU- FHWA project, addressed the noise issue by evaluating
conventional and innovative concrete pavement noise reduction methods in Europe and
the U. S.
1 6
In the U. S., conventional concrete pavement surface options for controlling tire- pavement
noise fall into two categories: 16
• Conventional texturing ( performed while concrete is still in a plastic state)
o Drag textures ( including artificial turf and burlap drag)
o Tined textures ( including transverse and longitudinal)
• Diamond grinding ( performed on hardened concrete pavement)
A brief definition is provided for each category along with examples and outcomes of
field studies or applications that relate to pavement noise reduction. A summary of the
pavement texture options presented in this subsection is provided in Table 5 on page 23.
2.3.1.1 Drag Texturing
Broomed surface textures are created by dragging a handheld or mechanical broom along
the surface of the pavement, creating a ridged surface. This texture typically consists of
1.5 to 3mm deep ( 0.06 to 0.12 in.) grooves, either longitudinal or transverse to the
centerline of the roadway.
Artificial turf drag surfaces are similarly created by dragging an inverted section of
artificial turf along the surface of the pavement. This technique often employs a device
that controls the time and rate of texturing, most commonly a construction bridge that
spans the pavement. Grooves of 1.5 to 3 mm ( 0.06 to 0.12 in.) in depth are typically
created. Burlap drag ( also known as Hessian drag) texturing is created by dragging
moistened, coarse burlap across the surface of the pavement, typically creating grooves
with depths between 1.5 and 3 mm ( 0.06 and 0.12 in.).
Studies have shown that dragged textures are sufficient for roadways with speeds below
72 km/ h ( 45 mph). More recent pavement evaluations in Minnesota have concluded that
the use of drag texturing results in comparable noise levels and surface friction to
conventional HMA pavements. The required texture depth specification in Minnesota is
reported to be 1.0 mm ( 0.04 in.) 16
According to Cackler et al., 16 the majority of concrete highway systems in Germany are
finished using a burlap drag texture. The burlap drag finish provides adequate friction and
minimizes air pumping. However, the frictional characteristics of the pavements often
decrease due to pavement wear. Use of larger sand particles may increase the texture life
by up to six years. The larger sand on the other hand may also reduce the concrete’s
workability.
Drag texturing techniques may provide a less costly and often quieter pavement than
other alternatives. Measures should be taken to ensure adequate friction, both initially and
during the service life. This can be achieved by selecting materials and mixes with
improved wear resistance.
1 7
2.3.1.2 Tined Texturing
Transverse tining is the most common texture on high- speed road and highway
pavements in North America. 19 It is produced by a mechanical device equipped with a
tining head ( metal rake) that moves laterally across the width of the paved surface. For
smaller areas, a hand rake is often used. Optimal dimensions vary from 10 to 40 mm ( 0.4
to 1.6in) spacing for random tines with no more than 50% above 25 mm ( 1.0in), 3 to 6
mm ( 0.12 to 0.24in) tine depth, and 3 mm ( 0.12in) tine width. 14,19 Skewing of tines has
been found to reduce tire- pavement interaction noise.
Favorable friction qualities of transverse tining are particularly pronounced in wet
weather conditions. Deep macrotexture is capable of reducing the water film thickness
resulting in reduced potential for hydroplaning. Depending on the properties of the
concrete mixture, transverse tining can provide beneficial frictional qualities over the life
of the pavement.
Transverse tining has also been known to exhibit undesirable noise emissions due to the
interaction between the pavement and vehicle tires. Noise emissions from transverse
tined textures depend on tine spacing, depth, and width. A study conducted by WIDOT in
2000 concluded that wider and deeper transverse tine textures often produce greater
noise. 15,16
A 1977 Minnesota DOT ( MDOT) report to the state legislature discussed the testing of
different anti- skid groove spacings on PCC pavement. By changing the spacing from 1.5
to 1.0 inch, roadside noise levels were reduced 2.5 to 4.0 dB. 20 Using results from a
Wisconsin study, MDOT was able to reduce its spacing to 0.75 inch achieving a further
reduction of 1.5 to 3.5 dB and an overall reduction of 4.0 to 7.5 dB. Wisconsin and
Minnesota also conducted noise studies on different types of bituminous pavements that
resulted in even greater noise reductions. Although no details are available about the data
collection process or the data analysis, it is assumed that transverse tining was the
texturing process applied to the PCC pavement in this study.
Uniform transverse tine spacings typically range from 12.5 to 25 mm ( 0.5 to 1 in).
“ Wheel whine” is often associated with uniformly spaced tines. While the dBA level of a
tined surface may not necessarily be higher than other texturing methods, the tonal nature
of the whine makes this pavement texture objectionable to many. To help mitigate the
tonal qualities, random tining is recommended. A broad range of random tine spacings,
between 10 to 76 mm ( 0.4 to 3 in.) has been reported to reduce noise emissions. In
situations where concrete finishing conditions are unfavorable ( e. g., objectionable
weather conditions and lack of equipment control), random spacings of 10 to 51 mm ( 0.4
to 2 in.) are recommended. The FHWA has recommended two random tining patterns,
averaging 13 mm and 26 mm ( 0.52 in. and 1.04 in.), respectively. 16 The shorter spacings
have been recommended to mitigate the high noise levels reported by some states that
have tried or adopted random spacings.
1 8
Skewing of transverse tining involves forming the grooves at an angle, rather than
perpendicular to the centerline. This is a complementary method that has demonstrated
benefits related to tire- pavement noise while providing the friction commonly associated
with transverse tined pavements. Research by Cackler et. al. identified a skew with a
recommended longitudinal- to- transverse ratio of 1: 6.16
Longitudinally tined textures are constructed in a manner similar to that of transverse
tining, except that the tining device is moved longitudinally along the direction of paving.
Although longitudinal tining is not used as frequently as transverse, it has been used
extensively in some states, including California.
Longitudinal tining is commonly reported to exhibit lower noise characteristics thereby
increasing its popularity and use. However, some transportation agencies have been
cautious to use this texturing technique because the data shows longitudinally tined
surfaces to have lower friction numbers when compared to transversely tined pavements,
all else being equal. One possible explanation of this may be the shape of the grooves
with respect to the traction forces of the tire ( compared to transverse tining). It should be
noted, however, that longitudinal tining on horizontal curves has been shown to prevent
vehicle skidding and thus improve safety. 16 Some DOTs report that if adequate cross-slope
exists, the differences between the surface drainage on transverse and longitudinal
tining are minimal.
Research shows that the long- term effectiveness of longitudinally tined surfaces is
impacted by the design of the pavement mix. Data have shown that longitudinally tined
pavements should contain a minimum of 25% siliceous sand to improve the level and
durability of the friction capacity.
The WIDOT study further concluded that among all of the concrete pavements evaluated,
those with longitudinal tining provided “ the lowest exterior noise while still providing
adequate texture”. When the texture is properly designed and constructed, longitudinally
tined pavements can achieve friction characteristics and durability comparable to either
transversely tined concrete pavements or dense- graded HMA pavements. 16
Volpe assisted California DOT in a comparison of three PCC test sections: longitudinal
tining, burlap dragged, and broomed tining. Volpe also assisted ADOT in comparing
uniform longitudinal tining, uniform transverse tining, and randomly spaced transverse
tining. Their findings showed that the quietest surface treatments were CA burlap
dragged, CA broomed, and AZ uniform longitudinal tining. 11
2.3.1.3 Diamond Grinding
Diamond grinding is a technique that removes a thin layer of hardened concrete
pavement using closely spaced diamond saw blades. The diamond saw blades are stacked
side- by- side and generally remove between 3 and 20 mm ( 0.12 and 0.8 in) from the
surface. The blades are gang- mounted on a cutting head and can generate 164 to 197
grooves/ m ( 50 to 60 grooves/ ft). Although diamond grinding has traditionally been used
to rehabilitate existing pavements by restoring smoothness, it has also been found to
1 9
reduce tire- pavement noise and restore pavement friction. The grinding procedure results
in the development of macrotexture. Furthermore, directional stability is more easily
controlled, making diamond grinding more appealing to drivers than longitudinal tining.
In one study conducted to compare transverse tining to longitudinal diamond- grinding,
test sections were constructed and evaluated for safety, noise, and other pavement
characteristics. 20 Diamond grinding was used to remove a thin layer of the concrete
surface. In some cases, thin fins of concrete were left behind and were subsequently
broken off by a blade. Each grinding head consisted of 166 saw blades, 3.18 mm ( 0.125
in.) separated by spacers with a thickness of 2.67 mm ( 0.105 in).
It has been reported that the key variables of diamond grinding are cutting blades, cut
depth, equipment horsepower, and the properties ( e. g., hardness) of the aggregates used.
In a 2001 study by Burgé, Travis, and Rado, the grinding rate was approximately 0.6
lane- km ( 0.4 lane- mi.) per day In addition, there was a specified minimum curing time of
seven days before grinding. KDOT conducted a study in 2004 and concluded that smaller
blade spacings led to reduced noise levels. 16
The study concluded that the longitudinal ground pavement was quieter than the
transversely tined pavement by 2 to 5 dBA ( measured on the side of the road). 16 When
noise measurements were conducted a year later, there was no real change in noise levels.
When comparing different vehicle types, the ground surface led to a 5- dBA noise
improvement for light trucks and automobiles, and a 2- dBA improvement for medium
and heavy trucks. The lower noise reduction for larger vehicles is believed to be due to
differences in the noise emission source; larger vehicles generate a greater percentage of
noise from the engine and exhaust systems ( as compared to tire- pavement noise
emissions). 16 Prior to making a decision on a pavement surface technology, the
percentage of heavy vehicles should be considered in determining overall effectiveness of
surface treatments.
Several states, including Arizona, California, New Jersey, North Dakota, and Virginia
have experience with tined and textured surfaces of PCC pavements in addressing
roadway noise. A partnership has been formed between California and the Western
States- ACPA on the I- 280 pavement rehabilitation project in San Mateo County. Noise
from old longitudinally tined pavement will be compared to noise from a PCC pavement
with diamond grinding, a PCC pavement with texture grinding, and a PCC pavement
overlain with 30 mm ( 1.17 in) of OGFC. 20 Noise measurements will be made for three to
five years to assess the longevity of noise reduction benefits.
The 2005 European scanning team recommended investigating and optimizing diamond-grinding
blade configurations to enhance the noise- reducing properties of existing
concrete surfaces in noise- sensitive locations. To achieve noise reduction texture should
always be negative ( pavement depressions). Positively textured pavements, such as chip
seals, increase noise. Positive texture is the magnitude of texture that exists above a
planar surface ( the riding surface). Positive texture almost always produces greater noise
with increasing texture depth. Chippings on concrete or exposed aggregate surfaces
could be considered the extreme case of positive texture.
2 0
Negative texture refers to the magnitude of the texture that exists below a planar surface.
A longitudinally grooved pavement would represent a negative texture. Negative textures
do not “ interfere” with the tire, resulting in less vibration and noise than a positive
texture. Therefore, the effect of negative texture is different from the effect of positive
texture. 21 This is another reason why texture depth alone cannot be used to correlate
noise across different pavement types.
2.3.1.4 Exposed Aggregate Concrete ( EAC)
EAC was discussed in the previous section as a concrete pavement treatment that is
usually applied using a two- layer “ wet on wet” paving process. It is the combination of
aggregates used in the top layer that determine its surface characteristics and texture.
Texture depths, curing solutions, and concrete finishing techniques are used to determine
the best combinations for optimal performance.
During the 2005 FHWA scanning tour, UK transportation officials reported that they
experimented with EAC finishes and found thin- layer quiet surfacings to be more cost
effective. Belgium uses EAC pavements and SMAs. Both have been optimized for noise.
The porous surfaces provide a slightly better noise benefit than SMA and EAC, but
officials believe that the latter provides a better blend of durability and noise reduction.
The Dutch province of Noord- Brabant conducted a study intended to further determine
the surface characteristics of EAC pavements. Various aggregates, texture depths, curing
solutions, and concrete finishing techniques were used in the study to determine the
combinations that provided optimal performance. Two Dutch aggregates, Dutch stone
and Graukwartsiet, were used in the study. The Graukwartsiet possessed a higher
polished stone value than the Dutch stone aggregate. Several texture depths were
evaluated. The standard depth was considered to be one- quarter of the maximum
aggregate size. Different retarding agents were evaluated, including lemon, acid
solutions, and various combinations of retarding agents and curing compounds. One- and
two- layer paving systems, as well as a super smoother ( finisher) were also evaluated in
the study. 16
Several key measurements and observations were made after construction. Texture depth
was found to be affected by the use of a super smoother, which resulted in a maximum
texture depth of 1.8 mm ( 0.07 in). When not used, texture depths were not as great, with
values commonly between 1.1 and 1.6 mm ( 0.04 and 0.06 in). The super smoother was
shown to produce positive effects in regards to noise emission, possibly due to a
reduction in megatexture. The selection of the retarding agent did not appear to make a
difference on the results. It was concluded that lower noise levels were measured when
smaller maximum aggregates were used.
A Swedish Study tested several concrete and HMA pavements for abrasion resistance,
friction, and noise under heavy traffic. The test sections were constructed with exposed
aggregates in the surface on both jointed plain and continuously reinforced concrete
pavements. Two different maximum aggregate sizes were used in the design of the
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concrete pavements, 8 and 16 mm ( 0.31 and 0.63 in). Noise was measured using the close
proximity ( CPX) method. In comparison to the HMA pavements constructed on the same
job, initial tests revealed that the EAC pavements with 16 mm ( 0.63 in) and 8 mm ( 0.31
in) stones provided noise levels that were 1.0 to 1.5 dBA and 3.0 to 3.5 dBA lower. 16
The noise emissions of the 16 mm ( 0.63 in) EAC and HMA sections were found to be
identical after one year. However, the 8 mm ( 0.31 in) EAC section actually produced
quieter noise levels after a year. Three years after construction, the noise levels from all
of the pavements had deteriorated. Also of interest was that during the winter season
concrete pavements produced noise levels about 1 dBA higher than the HMA pavements.
2.3.1.5 Pervious Concrete Pavements
Pervious concrete pavement was also discussed in the previous subsection as a pavement
treatment. A relationship between sound absorption and aggregate size was identified in
the research. In one study, a pavement with decreased aggregate size exhibited improved
sound absorption. A combination of # 4 and # 8 aggregates in the mixture exhibited
improved acoustic absorption characteristics when compared to straight gap grading. A
Belgian study reported sound reduction using pervious concrete as well, with a 5 dBA
decrease using a pervious concrete pavement with only 19% porosity. 16
Durability is commonly regulated by the interface of the two concrete layers and the
presence of pores. Once ice forms at the entrance of small pores and water is unable to
move, damage occurs very quickly. In pervious concrete, freezing tends to originate at
the top of the pavement and infiltrate into the lower depths of the layer. Differences in the
properties of the pervious and dense concretes can lead to stress concentrations at the
interface. The damage may take the form of an adhesion loss between the pervious
concrete and the conventional concrete. To combat this problem, continuous
maintenance and cleaning can be conducted to help preserve and restore the pavement’s
acoustical performance.
Double- layer pervious concrete has also been demonstrated as a possible solution where a
top lift with smaller aggregates is placed over a larger stone mix. The resulting system
may help to minimize infiltration of debris that causes clogging. The added cost of
constructing pervious concrete pavement must be taken into consideration. The long- term
effectiveness of this technique is still under debate. In one report by the Belgian Road
Research Centre it is noted that compared with a conventional concrete 22 cm ( 8.7 in)
thick a 4 cm ( 1.6 in) pervious concrete laid over 18 cm ( 7 in) of conventional concrete
has associated extra costs estimated at 40%”. However, no significant cost difference
was found with an equivalent structure including porous asphalt. The cost of constructing
quiet pervious concrete pavements in New Zealand has been reported at US $ 132 per m ²
( US $ 111 per sq. yd.). In the United States, pervious concrete projects have been reported
to cost 40% more. 16
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2.3.1.6 Innovative Pavement Texturing Solutions
In his research on concrete pavement noise reduction methods, Cackler identified several
innovative texturing solutions that were either being researched or were in experimental
stage. 16
• Stamping, Brushing, and Other Texturing Techniques: Other proposed
alternative texturing techniques are proposed to conventional tining, but will
be designed with better surface characteristic properties.
• Sprinkle Treatment: This technique is similar to EAC and distributes partially
embedded, small, polish- resistant stone chips on fresh concrete surface. This
technique was previously used in the U. S. in the 1970s and 1980s; however,
the equipment was rented from England, and therefore not available for wide-spread
application. Equipment will need to be developed or purchased.
• Shot Peening ( or shotblasting): Special equipment is used to propel tiny steel
shots onto the pavement surface. The shots make an imprint on the surface
and remove a thin layer of mortar and aggregate, exposing coarse aggregate.
An open porous surface texture is created increasing skid resistance and
reducing noise levels.
• Use of Helmholtz Resonators: Originally developed at the University of
Göttingen in Germany, euphonic pavements were designed as “ quiet tire/ road
combination” pavements, incorporating “ Helmholtz resonators underneath a
perforated but planed aluminum structure”. Helmholtz resonators are designed
to absorb low frequencies, typically ranging between 100 to 250 Hz.
Other potential texturing techniques identified by Cackler include: 16
• Paving concrete that possesses inclusions ( e. g., fiberglass, foam, and rubber particles)
to increase acoustical absorption,
• Application of acoustically absorptive materials for concrete shoulders ( as opposed to
traffic lanes), allowing for noise of all sources to be absorbed en route to the receiver
and also reducing surface wear and clogging issues,
• Quiet joint designs, addressing the significant factor of wheel “ slapping” at the joints
in overall noise levels,
• Dimpling, waffling, or other innovative geometries of fresh concrete texture,
• Textured profile pans, e. g. a corduroy pattern, for example, might be machined into
the profile pan of a slip- form paver to construct a surface similar to that resulting
from diamond grinding.
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Table 5: Summary of Concrete Pavement Texture Options16
Texture Description Current Use and Perception
Artificial turf
drag
Produced by dragging an inverted section
of artificial turf from a device that allows
control time and rate of texturing. Usually
a construction bridge that spans the
pavement typically produces 1/ 16 to 1/ 8
inch deep striations.
Artificial turf drag textures have shown sufficient friction
characteristics for many roadways, as well as reduced noise
relative to many transversely tined pavements. Minnesota has
used this type of texturing to reduce noise on high- speed roads.
Burlap drag Produced by dragging moistened coarse
burlap from a device that allows control of
the time and rate of texturing, usually a
construction bridge that spans the
pavement; typically produces 1/ 16 to 1/ 8
inch deep striations.
Burlap drag textures provide sufficient friction characteristics for
many roadways, especially those with speeds less than 45 mph,
and reduced noise relative to many transversely tined pavements.
This texture is used on Germany’s high- speed Autobahn system.
Transverse
tining
Produced by moving a mechanical device
equipped with a tining head across the
width of the paving surface laterally or on
a skew. Consistent concrete mixture and
constant forward movement of the paving
train at a uniform speed is required for a
consistent tining depth.
For tined pavements, texture depth and groove width are
important parameters in tire- pavement noise generation.
Pavements with uniformly spaced transverse tining generally,
but not always, exhibit undesirable “ wheel whine” noise.
Artificial turf or burlap drag texture precedes many projects.
Longitudinal
tining
Achieved by a mechanical device equipped
with a tining head ( metal rake) pulled in a
line parallel to the pavement centerline. For
consistent tining depth, maintain a
consistent concrete mixture and move the
paving train forward constantly at a
uniform rate of speed. Most projects
precede with an artificial turf or burlap
drag texture.
Tined texture depth and groove width are important parameters
in tire- pavement noise generation. Longitudinal tining is often
quieter than transverse tining. Narrower time spacings might be
used to reduce vehicle tracking and possibly reduce noise even
further. Lateral stability of narrow- tired vehicles may also
benefit from this.
Diamond
grinding
Longitudinal, corduroy- like texture made
by equipment using diamond saw blades
gang- mounted on a cutting head. About 50
to 60 grooves/ ft. are produced by the
cutting head 1/ 8 to ¾ inch is removed from
the pavement surface.
Diamond grinding has traditionally been used to restore
pavement smoothness, but has also been shown to reduce tire-pavement
noise and improve friction in the short term. Diamond
ground pavements do not affect vehicle tracking as much as
widely spaced longitudinally tined pavements.
EAC
pavement
European practice includes applying a set
retarder to the new concrete pavement and
then brushing or washing away mortar to
expose durable aggregates. Other
techniques involve the uniform application
of aggregates to the fresh concrete.
Regarded as an effective method for reducing tire- pavement
noise while providing adequate friction. Smaller aggregate sizes
have been reported to provide larger noise reductions, while
aggregates with a high polished stone value increase durability.
Only one large- scale EAC pavement project has been completed
in U. S.
Pervious
concrete
pavement
When used in highway applications,
pervious concrete is typically used as a top
layer ( wearing course), providing both low
noise emission and good drainage capacity.
The pervious concrete typically overlays a
conventional ( dense) concrete pavement
using a “ wet- on- wet” process.
Sound absorption increases with higher porosity levels for
pervious concrete, and also results from smaller aggregate sizes.
Use of pervious pavements for high- volume, high- speed
facilities is still in its infancy and will require more testing.
Regular maintenance and cleaning may be needed to prevent
clogged pores and to preserve the pavement’s acoustical
performance. Research on durability is ongoing in wet, hard-freeze
areas.
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2.3.2 Other Innovative Pavement Solutions
Traditionally, two- layer porous asphalt is laid in two passes – one pass per porous layer.
As a part of a Noise Innovation Program, equipment will be tested in the Netherlands to
construct two- layer porous asphalt in one pass – both layers being laid at the same time. 26
This technique is already in use in Germany with thin top layers. The objective of the
research is to determine if the “ one- pass placement” will increase the performance of the
two- layer pavement materials.
As a part of its Road to the Future program, 22 transportation researchers in the
Netherlands are focusing on long- term effects and the placement of pavement materials
using innovative and/ or fast construction techniques. Six experimental test sections have
been constructed:
a. The Very Silent Sound Module – this design has a functionally and physically
modular system. The sound- reducing functional modules contain Helmholtz
resonators. The road surface on top of the sound- reducing resonators is made of a thin
porous top layer. This single layer of asphalt has optimized surface properties, such as
low sound generation and a high skid resistance.
b. The Way of No Resound – this road design has three layers. Two top layers with a
combined thickness of 30 mm ( 1.2 in), are assembled in the factory as one roll- up
layer. The bottom layer is made up of concrete elements with a high supporting
power in which cavities that function as Helmholtz resonators are included. The pre-fabrication
of the top layer promotes a pavement surface without irregularities in the
macro- texture. This results in reduced vibration of a vehicle’s tires.
c. The Bonding Road – this design has a prefabricated asphalt mat on a roll that can be
bonded to or removed from the substrate very quickly by utilizing an “ on- off switch-ing”
bonding system. Prefabrication of the paving materials ensures a consistent high
quality end product. The bonding between the asphalt mat and the substrate can be
switched on or off by electromagnetic waves without any physical contact.
d. ModieSlab – the top layer of this road design consists of a 15 mm ( 0.6 in) open con-crete
layer, followed by another open concrete layer with coarsely broken gravel that
is 35 to 55 mm ( 1.4 to 2.2 in) thick. The thickness of the lower layer decreases from
the right to left lanes. Sound absorption is expected to match the type of lane traffic.
e. Quiet Transport – this road surface has porous asphalt with a very silent top layer.
During construction a special layer is installed to absorb engine noise. The pavement
design objective is to absorb both truck engine and tire noise.
f. Tapis Tolerance – the road construction for this pavement design includes a soft top
layer, a perforated compression layer, and an absorption layer of honeycomb profiles
in mineral wool. Due to the number of noise reducing elements, the expected noise
reduction potential is high, and more than likely the cost of road construction will
increase.
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Initial results for the pavement types tested under the Road to the Futures program are
shown in Table 6. These results reflect light vehicle traffic at 100 km/ h ( 62 mph). The
initial noise reduction levels reported for all pavement techniques vary between 5 and 7
dBA. The claimed reductions for some of the pavement techniques exceeded 10 dBA.
However, optimization of new pavement techniques may produce higher reduction levels.
Table 6: Initial Noise Reduction Levels for Light Vehicles
Road to the Future Project22
Pavement Technique Noise Reduction, dBA
Very Silent Noise Module 5
The Way of No Resound 6
The Bonding Road 6
ModieSlab 6 to 7
Quiet Transport 5 to 7
Tapis Tollerance 7 to 8
The 2005 FHWA Scanning Team noted the use of a single two- lift paver by Wirtgen
during their visit to Belgium. The Wirtgen paver allows for the use of lower- quality
aggregates in the base while using higher quality aggregates on the top surface. 13, 16,23
The two- lift process is not new to the U. S. and has been around almost as long as
concrete pavement. The two- lift paving technique was implemented extensively from
1950 to 1990 in many states to facilitate the placement of mesh in concrete during
interstate pavement construction. This pavement consisted of two layers placed wet on
wet, with the top layer consisting of a special surface mix. Beginning in the 1970’ s the
concrete paving industry moved away from a mesh dowelled design to a plain pavement
design, and shortening panels eliminated the need to pave with a two- lift process. Today
there are still some rare instances where the two- lift process is used in airport
construction to facilitate the placement of mesh between dowel baskets.
The two- lift process is used in Europe to develop a strong base pavement and a superior,
but thin, wearing surface. In France, continuous reinforced concrete pavement was
placed on two traffic lanes of highway A71 using the two- lift paving method. 23 The top
layer of this pavement, approximately 2 inches in depth, was made up of harder
aggregates. These aggregates provided low noise and high friction for the pavement
surface.
In Austria, the aggregate is secured with cement and then a two- inch layer of asphalt is
placed on top. The recycled aggregate is then mixed into the bottom 8.5 in deep concrete
layer, while the top 1.6 in deep layer was composed of a harder, higher quality
aggregate. The purpose of using a higher quality concrete for the top layer was to reduce
noise and increase friction, while keeping cost low by using a lower quality concrete for
the bottom layer. The case is very similar in Germany. Two- lift paving is often used to
reduce noise and increase friction. Germany also uses this method to reduce cost and
achieve a smoother profile. In addition, Germany has somewhat drastic climate changes,
which require the use of higher quality aggregate in the top layer to resist freezing and
thawing effects. 23
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The renewed interest in the two- lift process appears to be growing in the U. S.
Implementation of a two- lift system could help some agencies around the country
consume growing recycled asphalt piles, since most asphalt specifications only allow up
to 40% recycled asphalt in their product and generally only on the lower sections. If
recycled asphalt is available, it could be used to reduce costs as less of the more
expensive aggregates would need to be imported.
2.4 Other Considerations for Noise Source Reduction
Some methodologies that are being considered for pavement noise reduction do not fit in
any one of the three categories of interest identified in this study. Examples of such
methodologies include; developing a better understanding of the pavement attributes that
reduce noise generation for different vehicle types, evaluating pavement performance
with age, developing maintenance techniques that preserve the noise reducing
characteristics of pavement, and developing quieter tires without compromising safety.
At the InterNoise 2003 Conference, 22 transportation officials from The Netherlands
reported developing several projects under the Noise Innovation Program ( IPG) that
focused on the use of silent roads, improvement of tires and vehicles, optimization of
barriers, knowledge management, and facilities assessment methods. Their total budget
for noise abatement of road traffic is about 50 million euro. Looking to the future, one of
the keys to noise reduction from tire- pavement interaction on roadways in Arizona may
be the ability to model the effectiveness of combining several measures for a particular
application.
Sandberg identifies seven noise influencing road surface parameters ( Table 7) in an
international presentation to SILVA. 24 More interestingly, he notes that European
pavements are designed to be quiet, whereas California and Arizona pavements are off-the-
shelf.
Table 7: Noise Influencing Road Surface Parameters24
No. Parameter Degree of Influence
1 Macrotexture Very high
2 Megatexture High
3 Microtexture Low- moderate
4 Unevenness Minor
5 Porosity Very high
6 Thickness of layer High, for porous surfaces
7 Adhesion ( normal) Low/ moderate
8 Friction ( tangent.) See microtexture
9 Stiffness Uncertain (?), moderate
A significant finding reported by the 2005 FHWA Scanning Team is that the source level
of quiet pavements is being incorporated into existing highway noise prediction models
using varying methods. This effort falls under the Harmonised, Accurate, and Reliable
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Prediction Methods for the EU Directive on the Assessment and Management of
Environmental Noise ( HARMONOISE). The common EU model being developed will
incorporate pavement type in the prediction, along with other advanced prediction
parameters such as meteorological effects. 13 Pavement noise reductions of as little as 2
dB are being used in integrated noise strategies.
Under the European Union’s Environmental Noise Directive, adopted June 25, 2002, all
member countries are to:
a. Determine exposure to environmental noise through noise mapping,
including rural areas.
b. Use uniform prediction methods of assessment common to the members.
c. Ensure that information on environmental noise is made available to the
public.
d. Adopt action plans based on noise mapping results with a view toward
preventing and reducing environmental noise.
All member countries were to complete strategic noise maps and adopt actions plans on
or before June 30, 2007.
Many European highway paving projects are bid based on performance specifications.
The selection process is based on best- value contracting methods. Pavement vendors
have responded to agency performance criteria with innovative solutions that often carry
unequal risk, but if effective, can be held as proprietary for future project applications.
There appears to be large disagreement within the EU regarding effective maintenance of
negatively textured and highly porous pavements. Some countries require pressure
washing and vacuuming of the pavement at least twice a year, while others consider these
practices useless, or even harmful. Some countries have stopped using highly porous
pavements in snow and ice regions, and instead use SMA pavements with small
aggregate.
In the area or pavement noise research, an extensive amount of research on quiet
pavement technology is underway in the European Union and appears to be embedded in
the culture of the organizations. A research partnership exists between the transportation
agency and industry, and even with private entities. As an example, under the SIRIUS
program, companies are encouraged to submit innovative ideas that are judged by a panel
of topical experts. The best ideas are constructed as experimental sections. The selected
projects are highly sought after by companies as a marketing tool.
One of the recommendations from the 2005 scanning tour for US transportation
organizations was to consider reducing the aggregate size in the wearing surface of the
pavement to realize an immediate improvement in the noise- reducing properties of mixes.
In Europe, the aggregate sizes for quiet surfacing mixes are 4 to10 mm ( 0.16 to 0.4 in).
Most State DOTs use the Superpave aggregate gradings of 19, 12.5, or 9.5 mm ( 0.76, 0.5,
or 0.38 in). A drop in routine aggregate mix size to the next smallest gradation is
recommended and should produce a noise reduction of 1 to 3 dB. 13
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The emerging trend is to use thin- textured, gap- graded mixes with small aggregate in
urban or low- speed areas or areas subject to severe winter snow and ice accumulation.
The highly porous mixes are recommended for rural and high- speed roads with moderate
winter conditions. The European experience demonstrates that porous mixes are effective
in reducing noise when used properly. Early evaluation results in Europe indicate that
two- layer porous asphalt ( TLPA) appears to have potential application on high- speed
roads and produces exceptionally quiet pavements. Porous mixes should not be placed in
urban areas where the operating speed drops below 72 km/ h ( 45 mi/ h) since highly
porous mixes tend to clog under slow traffic.
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Section 3
Noise Reduction Survey
A survey questionnaire was developed to gather information from government and non-government
agencies regarding; a) current use and practices in the area of noise products,
materials, and technologies, b) current research on noise reduction methods, and c)
potential future use of noise reduction products, materials and/ or technologies. This
section of the report documents the methodology used to develop the survey questionnaire,
potential respondents targeted by the survey, and the execution of the survey. The survey
questionnaire results are discussed in Section 4.
3.1 Development of Questionnaire
The survey was designed to be short with no more than 10 questions. It was also designed
as an electronic survey to be distributed via email. Recipients had the option to mail back
the survey as a hard copy, if desired. The questions were arranged in the following order:
Leading Questions
Questions 1 through 4 were developed as leading questions that ask the potential
survey participant or “ respondent” about his/ her knowledge of different noise
products, materials, and technologies that were found in the literature review.
Budget
Question 5 asks the potential respondent to identify the amount ( or percentage) of
funds the their organization allocates for noise reduction projects on an annual basis.
Cost Benefit
Question 6 asks if a minimum reduction in decibels ( dB) is required before a noise
reduction project can be considered for implementation by the respondent’s organization.
Attribute
Question 7 asks how important certain attributes are when deciding to implement a
noise reduction project. Question 8 asks what attributes are important in deciding
against the implementation of a noise reduction measure or project?
Research
Question 9 asks whether the respondent’s organization was conducting any research on
the effectiveness of new noise reduction products, materials or technologies.
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Contact Information
In the event the research team had follow- up questions or needed clarification, each
respondent’s contact information was requested in Question 10.
3.2 List of Potential Respondents
One of the findings from the literature review was that the work of pavement noise
reduction has been primarily done by state transportation agencies, transportation related
organizations, universities, and consultants. This is not surprising, especially since the
nature of most road and highway work falls under the jurisdiction of state and local
governments. This narrows the list of potential respondents from a large sample population
to a very small one.
A list of potential survey respondents was created from state transportation organizations,
universities with transportation centers, professional associations, and vendors and sup-pliers
of noise reduction products. A list of 77 potential survey respondents was created.
3.3 Preliminary Noise Survey
A preliminary noise survey questionnaire was developed as a Microsoft Word document
and then converted to portable document format ( pdf). A cover letter and preliminary
survey questionnaire was e- mailed to 16 pre- survey respondents on February 24, 2006.
The 16 pre- survey respondents were selected from the list of 77 potential survey
respondents. A follow up response was sent to non- respondents about three weeks later.
The objective of the preliminary survey was to gain feedback/ input regarding the survey
form itself. Development of a preliminary survey prior to distribution of the full survey
allowed the study team to identify ambiguous questions, address formatting issues, and
correct possible deficiencies that may have been overlooked.
Each pre- survey respondent was asked to complete the attached preliminary survey
questionnaire and provide the study team with comments or other information regarding its
content and/ or structure. Another objective of the preliminary survey was to validate e-mail
addresses and other contact information for the pre- survey respondents.
If the pre- survey respondent had the ability to write to a pdf document, answers to the
preliminary survey questions could be made on the document, and emailed back to the
study team. If not, the pre- survey respondent was instructed to print a copy of the
preliminary survey, complete it and fax or mail it to the study team.
Two pre- survey respondents completed the preliminary pavement noise reduction survey
form and five pre- survey respondents provided comments. Each of the five pre- survey
respondents indicated that their organizations were not involved in noise reduction
research.
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3.4 Noise Reduction Survey
Minor changes ( mostly editorial or format related) were made to the preliminary pavement
noise survey questionnaire based on comments received. The final pavement noise
reduction survey was developed and e- mailed to the remaining 61 potential respondents as
well as the nine ( 9) pre- survey respondents who did not respond to the preliminary survey.
The first survey questionnaire was e- mailed on May 5, 2006 and a follow up mailing was
sent on May 16, 2006. Due to low response, a third e- mail was sent on June 28, 2006. All
non- respondents were called after the third mailing and encouraged to return the survey
questionnaire. If the individual was not in the office, a message was left on their voicemail.
Copies of the initial and follow- up cover letters and noise reduction survey questionnaire
are shown in Appendix 1.
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Section 4
Survey Results
This section provides a summary of the responses received from respondents who completed the
noise reduction survey questionnaire.
4.1 Overall Response Rate
Sixteen survey questionnaires were returned from the group of 77 potential respondents. This
represents a 20.9% overall response rate for the sample population. Of the 16 surveys that were
returned, two surveys were missing significant data. To not skew the data results, these two
surveys were eliminated from further analysis. Therefore, the effective sample size for the noise
reduction survey is 14 respondents.
4.2 Sample Validation
When a mail survey is conducted, there is no way to ensure that 100 percent of those surveyed
will respond to a questionnaire. For the Noise Reduction Survey, an e- mail survey was
considered to be the same as a regular postage mail survey. For some surveys, it is necessary to
conduct statistical tests to ensure that respondents are representative of the population, that there
is a minimum likelihood of response bias, and that the data are reliable. Statistical methods are
used to develop these answers. Due to the small sample population ( 77) and the even smaller
effective sample size ( 14), the data obtained from the Pavement Noise Reduction Survey is
statistically indeterminant. However, this in no way implies that the data obtained from the
survey is not useful to ADOT or other organizations.
This study utilizes the Convenient Survey methodology to assess respondents’ knowledge and
familiarity with products, materials, and technologies that are effective in reducing highway
noise. A Convenient Survey is very similar to a focus group that solicits opinions about a
particular product or service. It is less dependent on the sample size since one of its primary
purposes is to acquire knowledge and information related to a particular topic or subject matter.
Thus, the results from the 14 respondents in this study are comparable to what a targeted focus
group would provide.
4.3 Survey Results
Appendix 2 provides a detailed summary of the survey results.
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Section 5
Potential Growth of
Noise Reduction Measures
One of the findings of the literature review in Section 2 is the identification of several noise
reduction measures that are currently in use or undergoing research. Several European countries
have been engaged in pavement and other noise reduction measures associated with roadway
traffic since the 1980s or earlier. This comment was noted by several of the respondents in the
survey.
The results of the survey are documented in Section 4. Although limited, a few survey
respondents identified areas of future research and adoption by State DOTs with regard to traffic
noise products, materials, and technologies. In addition, these respondents indicated that a few
states such as California and Arizona have been at the forefront in researching noise reduction
methods. They noted that it is just recently that some of the other states have begun to consider
similar research activities in their transportation plans.
The objective of Task 4 of the Work Plan is to develop an assessment of the expected growth in
the acceptability and use of alternative noise reduction products, materials, and technologies.
This assessment is based on the findings from the literature review and the survey. Due to the
limited response from the survey, the assessment is largely based on findings from the literature
review.
5.1 Products
Noise wall barriers or sound walls have dominated this category for traffic noise reduction in the
United States, with approximately 165 million square feet of barriers as of 2004. Although this
category has shown growth over the years, continued growth of this traffic noise mitigation
measure is not expected in the future. The effectiveness of some sound walls has been called into
question, and is heavily tied to location and surrounding terrain.
Projected Growth: Replacement and repair of existing sound walls is required as part of routine
or ongoing maintenance. Growth in the variety of materials that can be used for sound walls will
continue, including the use of recyclable components. Those products that have been tested for
sound reduction with satisfactory results and are cost effective will continue to attract users.
Top coats and treatments for sound walls have been studied with mixed results. Further study in
this area is recommended for the potential to enhance the effectiveness of existing sound walls.
Use of modeling tools to enhance the design of existing and future noise walls is strongly
recommended.
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5.2 Materials
The noise reducing properties of OGFC, SMA, and HMA are well documented in the literature.
OGFC, which has been used in the warmer regions of Arizona, has a number of pavement noise
benefits. However, some of the shortcomings of this paving material are that it is not pervious to
rainwater, is not porous, and does not perform well in colder climates.
Projected Growth: The FHWA International Scanning Team ( IST) 13 provided a number of
recommendations for immediate implementation by transportation departments and other
organizations following their visit to five European countries in 2005 to review quiet pavement
practices. Two recommendations that were cited by the IST for immediate implementation are:
1. Two- layer Porous Mixes – early evaluation results in Europe indicate that TLPA
appears to have potential application on high- speed roadways and produces
exceptionally quiet pavements. Porous mixes should not be placed in urban areas
where the operating speed drops below 72 km/ hr ( 45 mi/ h) because highly porous
mixes tend to clog under slow traffic.
2. Reduce Aggregate Size – European practices show the aggregate sizes for quiet
surfacing mixes are between 0 and 4 mm ( 0.16 in) up to 0 and 10 mm ( 0.4 in).
Interestingly, most State DOTs use the Superpave aggregate gradings of 19 mm, 12.5
mm, or 9.5 mm ( 0.76, 0.5, or 0.38 in). Therefore, IST recommends a drop in routine
aggregate mix size to the next smallest gradation that could produce noise reductions
of 1 to 3 dB.
Since most of the quiet pavement work that has been completed to date in the U. S. has in
some way involved FHWA, those states that are just beginning to consider pavement
noise reduction projects are expected to seek guidance at the federal level and from other
more experienced State DOTs.
The benefits of NGOGFC were cited by TxDOT – good friction, lower noise, and in wet
weather: higher visibility, reduced splash and spray, reduced hydroplaning, and reduced
nighttime surface glare. ADOT and other State DOTs that are currently using OGFC
should also consider NGOGFC. NGOFC contains approximately 20% more asphalt by
volume than OGFC and has a minimum of 18% air voids. The void structure of
NGOGFC allows the mix to be more permeable and less likely to trap water. NGOGFC
appears to last twice as long as conventional OGFC. Although the problem of freezing in
colder climates has not been eliminated with NGOGFC, the pavement may hold up better
in cooler climates due to its more open graded mixture and thicker placement ( 1.5 to 2
inches vs. 1- inch for OGFC). NGOFC is 22.5% more expensive than OGFC. However,
the benefits and longevity may outweigh the additional costs.
The Netherlands has significant experience with double- layered porous asphalt construction. 11
Double- layer paving material consists of a bottom layer of coarse porous asphalt ( single- grained
gradation, aggregate size 11 to 16 mm ( 0.44 to 0.64 in) and a top layer of fine- graded porous
asphalt, aggregate size 4 to 8 mm ( 0.16 to 0.32 in)). Rubberized asphalt is used as the binder in
both layers. The double- layer porous mixture may also have applications for colder climates.
3 7
Although the extent of testing and application are limited, two materials that deserve more
investigation for their noise reducing properties are Italgrip and RCI. Each product has been used
with PCC to reduce highway levels. KDOT placed 3 inches of asphalt over a 1 inch RCI layer
across an eight- mile stretch of I- 435. Noise reduction levels of 7 dB were reported. Italgrip is a
very thin surface treatment consisting of a two- part polymer resin placed on the pavement
surface and covered with a man- made aggregate of re- worked steel slag 3 to 4 mm ( 0.12 to 0.16
in) in size. In a cooperative effort with the Highway Innovative Technology Evaluation Center
( HITEC), several states with different climatic conditions will test and evaluate the Italgrip
System. When available, ADOT should review these tests to further evaluate the effectiveness of
this thin surface treatment.
5.3 Technologies
One of the results from the literature review is a list of potential texturing techniques that
that may be effective in reducing tire- pavement noise. Another finding is a growing field
of techniques that are being studied to impart texture to pavement surfaces. Prior to
making a decision on a pavement surface texturing treatment, the percentage of heavy
vehicles should be considered in determining overall effectiveness of surface treatments.
Projected Growth: Pavement texturing recommendations cited by the IST13 are:
1. Thin- textured Surfacings – use of thin- textured surfacings with small aggregate size
is recommended for urban or low- speed roadway sections. To achieve noise
reduction, texture should always be negative ( pavement depressions).
2. Diamond- grinding – investigate and optimize the use of diamond- grinding blade
configurations to enhance noise- reducing properties of existing concrete surfaces in
sensitive locations.
3. EAC – research the use of EAC for construction of new concrete pavements.
Traditionally, transverse tining has been the most common texture on high- speed roads
and highway pavements in the United States. Longitudinal tining has been gaining in
acceptability and use and exhibits lower noise characteristics. Pavement design of
longitudinal tining ( minimum of 25% siliceous sand) is important to improve long- term
effectiveness.
Diamond grinding has been traditionally used to rehabilitate existing pavement and to restore
smoothness with the unexpected outcome of a quieter pavement. As recommended by Cackler, 16
“ only when the texture geometry can be characterized along with the corresponding noise and
other pavement surface characteristics will the optimum ‘ whisper grind’ technique be fully
realized.”
The technique of negatively texturing pavements, the equivalent of making a depression in the
pavement, is being perfected. According to Cackler, to move into the low- noise Zone 1, the
3 8
concrete pavement industry will have to embrace innovative solutions such as increasing
porosity, minimizing adverse texture wavelengths, or even modifying mechanical properties,
including stiffness. Successful products may include the use of pervious concrete, inclusions, and
polymers. Negative textured pavements are probably the only solution in Zone 1. Zone 1 is the
low noise level or “ innovation” zone, with on- board sound intensity ( OBSI) values at about 99 to
100 dBA and below range.
5.4 Other Measures
This report provides many examples of successful applications of traffic noise products,
materials, and technologies in the United States and other countries. However, noise or sound
reduction cannot be achieved by these measures alone. Effective land use planning is another
important component of successful reduction in highway noise. State DOTs should consider
encouraging local jurisdictions to enact noise ordinances and land use regulations to guide new,
noise- compatible development adjacent to major highways. 19
Another recommendation from IST is to update current noise policy and traffic noise models to
take advantage of the benefits of an integrated approach with other noise mitigation alternatives.
As reported at the InterNoise 2003 Conference, 21 transportation officials from The Netherlands
were developing several projects under the IPG that focus on an integrated approach - the use of
silent roads, improvement of tires and vehicles, optimization of barriers, knowledge management
and facilities and assessment methods – to achieve greater noise reduction. A similar approach is
strongly encouraged at the State DOT level.
3 9
Section 6
Conclusions and Recommendations
This research study was undertaken to compile information on traffic noise reduction
products, materials, and technologies that are currently available, and if appropriate to
this transportation agency’s needs, to assess what could be implemented with reasonable
effort. A review of the literature was undertaken. The research quickly identified large
volumes of information on traffic noise reduction measures. Traffic noise is defined here
as sound from the roadway that is heard as a result of vehicle use.
The regulation of many sources of noise, such as engine noise, blowing horns, noise from
residential or commercial buildings, etc. is outside the jurisdiction of a state
transportation agency. Most of the focus of this study was traffic noise reduction
products such as sound walls and sound wall treatments, as well as pavement noise
materials and technologies.
The literature review and noise survey identified measures that are being used by U. S.
transportation organizations as well as international efforts. Some key findings from the
literature review show the following best practices:
• Traffic Noise Reduction Products – noise or sound walls dominate this
category and have been used for decades in the U. S. The effectiveness of
sound walls has at times been called into question. Better design parameters
are needed to ensure that noise is properly deflected away from receptors.
However, existing noise walls have to be maintained and sometimes replaced.
Findings from the literature revealed a variety of materials to choose from that
are both aesthetically attractive, and effective in reducing noise from highway
vehicle use. The cost of installing products will need to be evaluated on a case
by case basis with the vendor or for each applicable product.
• Traffic Noise Reduction Materials – The operating speed of the roadway
should be factored into the roadway design for quiet pavements. European
studies show that higher porous mixtures tend to clog under slower speeds
( less than 72 km/ hr, 45 mph).
• Two layer- porous mixes have been found to be effective in Europe and the
U. S. An important attribute for consideration in two layer- porous mix design
and placement is aggregate size. Most State DOTs use the Superpave
aggregate gradings of 19 mm, 12.5 mm, or 9.5 mm ( 0.76, 0.5, or 0.38 in).
Current recommendations are to drop the routine aggregate mix size to the
next smallest gradation, with an expectation of reducing noise levels 1 to 3 dB.
4 0
• Pavement Noise Reduction Technologies - use of thin- textured surfacings
with a negative pavement depression are recommended for urban or low-speed
roadway sections. Diamond grinding enhances noise reduction on
concrete surfaces in sensitive locations.
• Other Pavement Noise Reduction Measures – looking forward, transportation
officials are encouraged to develop an integrated approach to roadway noise
reduction. Instead of relying on a single measure, the recommended strategy is
to develop the ability to model the effectiveness of a number of different
measures.
EAC and pervious concrete pavements have been identified as promising innovate
concrete solutions. These technologies require further study or specification development
before becoming part of paving practices in the United States.
Looking forward, a number of innovative traffic noise research programs are currently
underway, both in the United States and Europe. As an example, the Netherlands is
developing several silent pavement projects under their Noise Innovation Program. These
projects not only focus on pavement materials or texturing techniques, but also
improvement of tires and vehicles, knowledge management, and assessment methods.
The outcomes of these projects should be documented to determine if they are applicable
and cost effective for use on Arizona’s highways.
Many State DOTs’ noise reduction programs are in their infancy. Those states that have
established programs for noise reduction within the last decade ( including Arizona) will
be sought after for their expertise in the area, including pavement noise reduction.
41
List of References
1. Manuel, John. 2005. “ Clamoring for Quiet; New Ways to Mitigate Noise”.
Environmental Health Perspectives 113( 1).
2. FHWA Noise team. 2001. Keeping the Noise Down: Highway Traffic Noise
Barriers. Washington D. C. Agency report.
3. Federal Highway Administration ( FHWA). 2006. Highway Traffic Noise in the
United States: Problems and Response. Agency Report.
http:// www. fhwa. dot. gov/ environment/ probresp. htm, viewed Oct. 02, 08.
4. www. acoustics. com, web definition. Viewed June 15, 2006
5. Butler, G. F. 1974. “ A note on improving the attenuation given by a noise
barrier”. Sound and Vibration, 32( 3) 367- 369.
6. Mongeau, Luc, J. Stuart Bolton, and Sanghoon Suh. 2003. Investigation of Novel
Acoustic Barrier Concepts Phase I: Concept Development and Preliminary
Evaluation. Final Report:. The Institute for Safe, Quiet, and Durable Highways,
Purdue University.
7. Same as reference # 6 above.
8. Same as reference # 6 above.
9. Rubber Pavements Association. 2000 ( Summer). Newsletter 2 ( 2),
http:// www. asphaltrubber. org/ RPA_ Newsletters/ summer2000/ page4. html Last
viewed July 14, 2008
10. Kandhal, P. S. 2004. “ Asphalt Pavements Mitigate Tire/ Pavement Noise”, Hot
Mix Asphalt Technology. March/ April Ed.
11. Venner Consulting and Parsons Brinckerhoff. 2004. Compendium of
Environmental Stewardship Practices, Procedures, and Policies for Highway
Construction and Maintenance. NCHRP Project Report 25- 25( 04).
12. Fults, Ken et. al. June 2005. Cold Weather Performance of New Generation
Open Graded Friction Courses. Austin, Texas. Project 04- 834. Presentation.
13. Federal Highway Administration. 2005. Quiet Pavement Systems in Europe.
International Technology Exchange Program, Report No. FHWA- PL- 05- 011
14. Kansas DOT. 2005. KDOT’s I- 435 Project Provides Good Road, Quiet
Alternative. Hot Mix Asphalt Technology Source
15. Kuemmel, David et al. 2000. Investigative Study of the Italgrip System: Noise
Analysis. Report Number WI/ SPR- 02- 00. Wisconsin Department of
Transportation.
16. Cackler, E. Thomas. July 2006. Evaluation of U. S. and European Concrete
Pavement Noise Reduction Methods. Iowa State University. National Concrete
Pavement Technology Center.
42
17. Meiarashi, Seishi. 1996. Porous Elastic Road Surface as an Urban Highway
Noise Measure. Tsukuba Ibaraki Japan. Public Works Research Institute.
18. Dutch/ Danish Delegation. 2006. Noise Reducing Pavements in Japan.
http:// www. vejdirektoratet. dk/ publikationer/ VInot031/ index. htm Study Tour
Report. Viewed July 14, 2008.
19. American Concrete Pavement Association. 2005. ACPA Concrete Pavement
Progress. 41 ( 7).
20. Marsella, Mark. December 1997. Reduction of Traffic Noise at the Source. New
Jersey Department of Transportation.
21. American Concrete Pavement Association. October 2006. “ Rules of Thumb on
Pavement Noise,” Concrete Research & Technology. 7.
22. Hoffman, Rob and Jasper van der Kooij. 2003. Results from the Dutch Noise
Innovation Program Road traffic ( IPG) and Roads to the Future Program
( WnT)”. 32nd International Congress and Exposition on Noise Control
Engineering. Netherlands.
23. Cable, James K. and James P. Fentress. 2004. Two- Lift Portland Cement Concrete
Pavements to Meet Public Needs. Final Report. Iowa State University.
24. Sandberg, Ulf. August 2005. Low Noise Road Surfaces, State- of- the- Art.
Presentation at EU Project Silenda Via ( SILVIA), International Seminar, Swedish
Road and Transportation Institute. Brussels, Belgium.
43
Appendix 1
Selected Noise Reduction Survey Documents
• Survey Cover Letters Page 45
• Survey Document Page 47
44
45
46
47
48
49
50
51
Appendix 2
Noise Reduction Survey Resposes
ADOT Transportation Research Center
Figure A2- 1: Noise Reduction Survey
Summary of Responses
1. How familiar are you with the following Sound Abatement Products, Materials or Technologies?
Don’t Not Somewhat Very Extremely
Know Familiar Familiar Familiar Familiar Familiar
Pavement Alternatives
- Dense grade asphalt 1 2 0 8 2 1
- Rubberized pavement 0 2 5 3 4 0
- Portland cement concrete 0 0 4 4 6 0
- Other 7 1 3 3 0 0
Traffic Noise Barriers
- Sound Absorbing Noise Walls 0 0 1 6 5 2
- Earth Mounds or Berms 0 0 0 7 5 2
- Other 8 3 1 1 1 0
Traffic Noise Barrier Treatment
& Coatings
- Crumb rubber 0 6 4 1 2 1
- Innovative noise barrier design 1 4 4 3 2 0
- Other 8 3 1 1 1 0
Receptor Controls
- Land Use Planning 0 0 8 1 3 2
- Window Treatments 0 4 7 2 1 0
- Other 8 4 0 2 0 0
2. How effective are the following Products, Materials, or Technologies in reducing
pavement and traffic noise?
Don’t Not Somewhat Very Extremely
Know Effective Effective Effective Effective Effective
Pavement Alternatives
- Dense grade asphalt 1 2 1 7 2 1
- Rubberized pavement 0 1 7 4 1 1
- Portland cement concrete 1 1 4 6 2 0
- Other 7 3 2 0 1 1
Traffic Noise Barriers
- Sound Absorbing Noise Walls 2 2 2 6 1 1
- Earth Mounds or Berms 1 1 3 4 1 4
- Other 8 3 2 0 1 0
52
Traffic Noise Barrier Treatments
& Coatings
- Crumb rubber 6 0 1 6 0 1
- Innovative noise barrier design 1 4 1 2 6 0
- Other 8 5 0 0 0 1
Receptor Controls
- Land Use Planning 1 0 6 3 1 3
- Window Treatments 1 3 7 3 0 0
- Other 2 6 4 0 1 1
3. If you are familiar with the following brands or products listed below, how would you
rank their effectiveness in reducing highway pavement noise?
Don’t Not Somewhat Very Extremely
Know Effective Effective Effective Effective Effective
Products
SoundSorb 8 0 0 4 0 0
Whisper Wall 10 0 1 1 0 0
Quilite Walls 11 0 1 0 0 0
Carsonite Sound Barrier System 8 0 1 2 1 0
Paraglas Sound Stop 9 0 0 3 0 0
AcoustaCrete 10 1 0 1 0 0
Crumb Rubber Coatings 9 0 1 2 0 0
Top Treatment ( for sound barriers) 11 0 1 0 0 0
NOISHIELD 12 0 0 0 0 0
Starkustic 12 0 0 0 0 0
Soundblox 10 0 1 1 0 0
Broad Band Sound Absorber 11 0 0 0 1 0
Perma Delta Sound Barrier 12 0 0 0 0 0
Coustiview 12 0 0 0 0 0
Materials
Porous Friction Course 2 0 3 4 2 2
Dense Graded Hot Mix Asphalt 2 1 7 2 1 0
Stone- Matrix Asphalt Concrete 5 1 2 3 2 0
Street Absorbing Membrane
Interlayer 10 0 0 2 0 0
Portland Cement Concrete 2 4 3 3 1 0
Technologies
Hot Mix Asphalt 3 2 5 0 2 1
Surface Texturing 3 0 3 4 2 1
Bonding Road 11 0 2 0 0 0
Modieslab 12 0 0 1 0 0
53
4. Do you know other noise reduction Products, Materials, or Technologies not listed above?
Please list their names below.
5. On the average, what percentage of your highway budget is allocated for noise reduction
measures in highway projects? 10 respondents reported a range of 1 to 5% ( average of 2.1%) of their
highway budget is allocated for noise reduction measures.
6. Does your Agency require a “ noise benefit factor” before implementing sound reduction
measures? Example, a noise benefit of three ( 3) decibels is required before implementing sound
reduction measures in a highway project.
10 respondents said “ Yes”, 1 respondent said “ No”, and 2 respondents said it “ Varies by Project”
7. How important are the following in considering and implementing sound abatement measures in
your highway projects:
Not Somewhat Very Extremely
Important Important Important Important Important
Cost Effectiveness 0 0 0 11 3
Technology Maturity 0 1 6 4 3
Durability 0 0 2 6 6
Low Cost and Convenience
in Installation 0 5 3 5 1
Low Cost, Convenience
in Maintenance & Repair 0 4 3 5 2
Aesthetics 0 0 9 5 0
8. When it come to your agency NOT using hot mix asphalt and other Technologies to abate traffic
noise, how important are:
Not Somewhat Very Extremely
Important Important Important Important Important
Cost Effectiveness 1 0 4 5 2
Technology Maturity 1 1 4 4 2
Durability 1 0 2 8 1
Low Cost and Convenience
in Installation 1 3 2 5 1
Low Cost and Convenience
in Maintenance & Repair 1 2 4 4 1
Federal Guidelines ( not QPPP approved ) 4 0 4 2 1
More Research and Testing Needed 0 2 5 2 3
Products Materials Technologies
Other 1 Durisol Precast Concrete Planting buffers
Evergreen Wall Recycled plastic
Nova Chip
Other 2 Hoover Wall ( wood) No response Site design
Other 3 No response No response No response
54
9. Is your Agency currently conducting research or studying the effectiveness of new noise
reduction Products, Materials or Technologies?
13 respondents said: No = 5, Yes = 8, No Response = 1
If yes, list:
Products Materials Technologies
Item 1: Durisol Sound Absorptive - 1 Rubberized pavement - 1 Texturing - 2
Nova Chip - 1 OBSI* - 1
Item 2:
Item 3: Pavement types - 1
* OBSI – On board sound intensity ( for noise measurement)
10. May we contact you in the future, concerning noise reduction, Products, Materials or
Technologies?
Name of Organization: _____________________________________
Contact Person: _______________________________________
Phone Number: _______________________________________
Email Address: _______________________________________
Thank you very much for your time and consideration in assisting us with this project.
55
A discussion of the Pavement Noise Reduction Survey is presented in this appendix. A
summary of the responses to the Pavement Noise Survey questionnaire is provided in
Figure A4- 1.
A. 2.1 Knowledge of Products, Materials, or Technology
Question 1: How familiar are you with the following Sound Abatement Products,
Materials or Technologies?
Most of the respondents reported being somewhat to extremely familiar with each
pavement noise reduction product, material or technology listed under Question 1.
The most responses were reported for:
o Pavement Alternatives: Dense grade asphalt – 8 Familiar ( 57.1%)
o Traffic Noise Barriers: Earth mounds or berms – 7 Familiar ( 50.0%)
o Receptor Controls: Land use planning – 8 Somewhat Familiar ( 57.1%)
o Receptor Controls: Window treatments – 7 Somewhat Familiar ( 57.1%)
No additional responses were provided for “ Other” pavement alternatives, traffic
noise barriers, traffic noise barrier treatment and coatings, or receptor controls.
Question 2: How effective are the following Products, Materials, or Technologies in
reducing pavement and traffic noise?
Respondents were asked to identify the effectiveness of each noise reducing
product, material, or technologies listed:
o Pavement Alterations:
􀂃 Dense grade asphalt – 7 Effective ( 50.0%)
􀂃 Rubberized pavement – 7 Somewhat Effective ( 50%)
o Traffic Noise Barriers: Sound absorbing noise walls – 6 Effective ( 42.9%)
Additional Comments: TxDOT has only used absorptive treatment on
an experimental basis. The research work focused on construction
techniques rather than acoustical properties. TxDOT has rarely
considered/ used earth mounds/ berms due to insufficient right- of- way
for construction.
o Traffic Noise Barrier Treatment and Coatings:
􀂃 Crumb rubber – 6 Don’t Know ( 42.9%) and 6 Not Effective ( 42.9%),
o Receptor Controls: Window Treatments – 7 Somewhat Effective ( 50%)
Additional Comments: TxDOT has developed a comprehensive
presentation on “ Noise Compatible Land Use Planning.”
No additional responses were provided for “ Other” pavement alternatives, traffic noise
barriers, traffic noise barrier treatments and coatings, or receptor controls.
56
Question 3: If you are familiar with the following brands or products listed below, how
would you rank their effectiveness in reducing highway pavement noise?
A list of some of the pavement noise reducing products, materials or technologies
identified in the literature review were included in this question. Not surprisingly, most
respondents checked “ Don’t Know” for the list of products. Four ( 28.6%) of the
respondents indicated that the noise barrier product, SoundSorb, is somewhat Effective.
For the Materials listed, 7 ( 50%) identified dense graded hot mix asphalt ( DGAC) as
“ Somewhat Effective” at reducing pavement noise, and 10 respondents ( 71.4%) chose
“ Don’t Know” when asked about the effectiveness of a street absorbing membrane
interlayer.
Although HMA is considered a paving material, it is also included as a technology due to
the process used to place the pavement. Five ( 5) respondents identified HMA as
“ Somewhat Effective” as a pavement noise reduction technology.
Question 4: Do you know other noise reduction Products, Materials, or Technologies
not listed above? Please list their names below.
When asked about the respondent’s knowledge of other pavement noise reduction
products, materials, or technologies that were not listed in Questions 1 to 3, only
three of 14 respondents provided additional information. Some items provided by
the respondents are improperly categorized, e. g. planting buffers and site design
are not technologies, however, these responses are included in information
reported in the literature review
57
Question 5: On average, what percentage of your highway budget is allocated for noise
reduction measures in highway projects?
Eleven ( 78.6%) of the 14 respondents reported that 1 to 5% ( average of 2.1% for survey)
of their department’s budget is allocated for noise reduction activities ( see Figure A4- 2

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SURVEY OF TRAFFIC NOISE
REDUCTION PRODUCTS,
MATERIALS, AND
TECHNOLOGIES
Final Report 584
Prepared by:
Vi Brown
Prophecy Consulting Group, LLC
2005 S. Henkel Circle
Mesa, AZ 85202- 6564
December 2008
Prepared for:
Arizona Department of Transportation
206 South 17th Avenue
Phoenix, Arizona 85007
In cooperation with
U. S. Department of Transportation
Federal Highway Administration
The contents of the report reflect the views of the authors who are responsible for the facts and
the accuracy of the data presented herein. The contents do not necessarily reflect the official
views or policies of the Arizona Department of Transportation or the Federal Highway
Administration. This report does not constitute a standard, specification, or regulation. Trade or
manufacturers’ names which may appear herein are cited only because they are considered
essential to the objectives of the report. The U. S. Government and The State of Arizona do not
endorse products or manufacturers.
This report can also be found on our web site…
http:// www. dot. state. az. us/ ABOUT/ atrc/ Publications/ Publications. htm
Technical Report Documentation Page
1. Report No.
FHWA- AZ- 08- 584
2. Government Accession No.
3. Recipient's Catalog No.
4. Title and Subtitle
5. Report Date
December 2008
Survey of Traffic Noise Reduction Products, Materials, and
Technologies
6. Performing Organization Code
7. Author
Vi Brown
8. Performing Organization Report No.
9. Performing Organization Name and Address
10. Work Unit No.
Prophecy Consulting Group, LLC
2005 S. Henkel Circle
Mesa, AZ 85202- 6564
11. Contract or Grant No.
T0549A0028
12. Sponsoring Agency Name and Address
ARIZONA DEPARTMENT OF TRANSPORTATION
206 S. 17TH AVENUE
13. Type of Report & Period Covered
FINAL REPORT
April 2005 – February 2008
PHOENIX, ARIZONA 85007
Project Manager: Estomih M Kombe, PhD, PE
14. Sponsoring Agency Code
15. Supplementary Notes
Prepared in cooperation with the U. S. Department of Transportation, Federal Highway Administration
16. Abstract
Noise is one of the most pervasive forms of environmental pollution. It is everywhere and affects our lives at
home, work and play. By definition, noise is any unwanted or excessive sound. Highway traffic noise is a
major issue for transportation agencies. The objective of this study was to identify noise reduction products,
materials, and technologies currently available and that may have potential as noise mitigation alternatives.
The literature review and survey identified measures that are being used by U. S. transportation organizations
as well as international efforts. Some key findings from the literature review show the following best
practices:
- Pavement Noise Reduction Products – noise or sound walls dominate this category and have been used
for decades in the U. S. Findings from the literature revealed a variety of materials to choose from that are
both aesthetically attractive, and effective in reducing sound from tire pavement noise. The cost of installing
products will need to be evaluated on a case by case basis with the vendor or for each applicable product.
- Pavement Noise Reduction Materials – The operating speed of the roadway should be factored into the
roadway design for quiet pavements. European studies show that higher porous mixtures tend to clog under
slower speeds. Two layer- porous mixes have been found to be effective in Europe and the US. An
important attribute for consideration in two layer- porous mix design and placement is aggregate size.
- Pavement Noise Reduction Technologies - use of thin- textured surfacings with a negative pavement
depression are recommended for urban or low- speed roadway sections. Diamond grinding enhances noise
reduction on concrete surfaces in sensitive locations.
- Other Pavement Noise Reduction Measures – looking forward, transportation officials are encouraged to
develop an integrated approach to roadway noise reduction. Instead of relying on a single measure, the
recommended forward strategy is to develop the ability to model the effectiveness of a number of different
measures to achieve greater noise reduction.
17. Key Words
Noise Barriers, Noise Walls, Roadway Noise
Mitigation, Vehicle Noise, Highway Noise
Reduction
18. Distribution Statement
Document is available to the
U. S. public through the
National Technical Information
Service, Springfield, Virginia
22161
23. Registrant's Seal
19. Security Classification
Unclassified
20. Security Classification
Unclassified
21. No. of Pages
86
22. Price
SI* ( MODERN METRIC) CONVERSION FACTORS
APPROXIMATE CONVERSIONS TO SI UNITS APPROXIMATE CONVERSIONS FROM SI UNITS
Symbol When You Know Multiply By To Find Symbol Symbol When You Know Multiply By To Find Symbol
LENGTH LENGTH
in inches 25.4 millimeters mm mm millimeters 0.039 inches in
ft feet 0.305 meters m m meters 3.28 feet ft
yd yards 0.914 meters m m meters 1.09 yards yd
mi miles 1.61 kilometers km km kilometers 0.621 miles mi
AREA AREA
in2 square inches 645.2 square millimeters mm2 mm2 Square millimeters 0.0016 square inches in2
ft2 square feet 0.093 square meters m2 m2 Square meters 10.764 square feet ft2
yd2 square yards 0.836 square meters m2 m2 Square meters 1.195 square yards yd2
ac acres 0.405 hectares ha ha hectares 2.47 acres ac
mi2 square miles 2.59 square kilometers km2 km2 Square kilometers 0.386 square miles mi2
VOLUME VOLUME
fl oz fluid ounces 29.57 milliliters mL mL milliliters 0.034 fluid ounces fl oz
gal gallons 3.785 liters L L liters 0.264 gallons gal
ft3 cubic feet 0.028 cubic meters m3 m3 Cubic meters 35.315 cubic feet ft3
yd3 cubic yards 0.765 cubic meters m3 m3 Cubic meters 1.308 cubic yards yd3
NOTE: Volumes greater than 1000L shall be shown in m3.
MASS MASS
oz ounces 28.35 grams g g grams 0.035 ounces oz
lb pounds 0.454 kilograms kg kg kilograms 2.205 pounds lb
T short tons ( 2000lb) 0.907 megagrams
( or “ metric ton”)
mg
( or “ t”)
mg megagrams
( or “ metric ton”)
1.102 short tons ( 2000lb) T
TEMPERATURE ( exact) TEMPERATURE ( exact)
º F Fahrenheit
temperature
5( F- 32)/ 9
or ( F- 32)/ 1.8
Celsius temperature º C º C Celsius temperature 1.8C + 32 Fahrenheit
temperature
º F
ILLUMINATION ILLUMINATION
fc foot candles 10.76 lux lx lx lux 0.0929 foot- candles fc
fl foot- Lamberts 3.426 candela/ m2 cd/ m2 cd/ m2 candela/ m2 0.2919 foot- Lamberts fl
FORCE AND PRESSURE OR STRESS FORCE AND PRESSURE OR STRESS
lbf poundforce 4.45 newtons N N newtons 0.225 poundforce lbf
lbf/ in2 poundforce per
square inch
6.89 kilopascals kPa kPa kilopascals 0.145 poundforce per
square inch
lbf/ in2
SI is the symbol for the International System of Units. Appropriate rounding should be made to comply with Section 4 of ASTM E380
v
Table of Contents
Page
Section 1 - Introduction ........................................................................................... 1
1.1 Scope of Work ....................................................................................... 1
1.2 Report Organization............................................................................... 3
Section 2 – Literature Review.................................................................................. 5
2.1 Noise Reduction Products...................................................................... 5
2.2 Noise Reduction Materials..................................................................... 8
2.3 Noise Reduction Technologies ............................................................ 15
2.4 Other Considerations for Noise Source Reduction.............................. 26
Section 3 – Noise Reduction Survey .................................................................... 29
3.1 Development of Questionnaire ............................................................ 29
3.2 List of Potential Respondents .............................................................. 30
3.3 Preliminary Noise Survey.................................................................... 30
3.4 Noise Reduction Survey ...................................................................... 31
Section 4 – Survey Results .................................................................................... 33
4.1 Overall Response Rate......................................................................... 33
4.2 Sample Validation................................................................................ 33
4.3 Survey Results ..................................................................................... 33
Section 5 – Potential Growth of Noise Reduction Measures................................. 35
5.1 Products................................................................................................ 35
5.2 Materials .............................................................................................. 36
5.3 Technologies........................................................................................ 37
5.4 Other Measures .................................................................................... 38
Section 6 – Conclusions and Recommendations ................................................... 39
List of References .................................................................................................. 41
Appendix 1 Selected Noise Reduction Survey Documents............................... 43
Appendix 2 Noise Reduction Survey Responses............................................... 51
Appendix 3 A Sampling of Traffic Noise Reduction Products ......................... 61
v
List of Tables
Title Page Number
Table 1 Total Noise Barrier Area by Material Type ( through 2004)............................ 7
Table 2 Noise Barrier Data for United States ( through 2004) ...................................... 7
Table 3 Noise From Different Pavement Surface Types ( International Studies) ......... 9
Table 4 Noise From Different Pavement Surface Types ( National Studies).............. 10
Table 5 Summary of Concrete Pavement Texture Options ........................................ 23
Table 6 Initial Noise Reduction Levels for Light Vehicles Road
to the Future Project....................................................................................... 25
Table 7 Noise Influencing Road Surface Parameters ................................................. 26
v
Glossary
Abbreviations
e- mail electronic mail
Symbols
ρ density
λ lambda ( wavelength)
μ micro
Units of Measurement
Sound
AC absorption coefficient
c speed of sound
CCA chromated copper arsenate
CNEL Community noise equivalent level
dB decibels
dBA decibels, A- weighted sound level
ITC Indoor Transmission Class
L level
Ldn Day- night noise level
Leq Equivalent noise level
Lmax Maximum noise level
Lx noise level exceeded by “ x” percent
NHDOT New Hampshire Department of Transportation
NRC Noise Reduction Coefficient
PSL pressure sound level
SEL single event level
STC Sound Transmission Class
STL Sound Transmission Loss
Other units of measurement
oC degree Celsius
oK degree Kelvin
cm centimeter
f frequency
ft feet
h hour
Hz hertz
in inch
kg kilogram
km kilometer
km/ h kilometer/ hour
LF linear feet
m meter
m2 square meter
m3 cubic meter
mi mile
mm millimeter
MPa 106 or 1 million Pascal
mph mile/ hour
N Newton
Pa Pascals
rms root mean square
s second
SF square feet
sq. yd. square yard
SQRT square root
P pressure
PLF pound per linear foot
pcf pound per cubic foot ( lbs/ ft3)
psi pound per square inch ( lbs/ in2)
psf pound per square feet ( lbs/ ft2)
W Watt
Acronyms
AASHTO American Association of State Highway and Transportation
Officials
ACPA American Concrete Paving Association
ADOT Arizona Department of Transportation
AMT Advanced Masonry Technology
ASI Acoustical Solutions, Inc.
ASTM American Society for Testing and Materials
ATRC Arizona Transportation Research Center
CPX close proximity
CRCP continuously reinforced concrete pavement
CSI Concrete Solutions, Inc.
DGAC dense graded asphalt concrete
DOT Department of Transportation
EAC exposed aggregate concrete
EPA Environmental Protection Agency
FHWA Federal Highway Association
FMCSA Federal Motor Carrier Safety Administration
HARMONOISE Harmonized, Accurate, and Reliable Prediction Methods for the
EU Directive on the Assessment and Management of
Environmental Noise
HITEC Highway Innovative Technology Evaluation Center
HMA hot mix asphalt
IPG Innovation Program ( Netherlands)
ISU Iowa State University
IST International Scanning Team
GVWR Gross Vehicle Weight Rating
KDOT Kansas DOT
MDOT Minnesota DOT
NCAT National Center for Asphaltic Technology
NCHRP National Cooperative Highway Research Program
NGOGFC new generation open graded asphalt friction course
OBSI on- board sound intensity
OGFC open graded asphalt friction course
OSHA Occupational Safety and Health Association
PERS porous elastic road surface
PIARC Permanent International Association of Road Congresses – the
previous name for the organization that is now known as the
World Road Association
PCC Portland cement concrete
PFC porous friction course
PWRI Public Works Research Institute ( Japan)
QPPP Quiet Pavement Pilot Program
QUASH ™ QUASH, a trademark of the Dow Chemical Company for a large
cell polyethylene foam product that is typically used for sound
absorption.
RFI reflective cracking interlayer
RFP request for proposal
SILVIA Silenda Via Project
SIRIUS Silent Roads for Urban and Extra- Urban Use ( European Union)
SMA stone matrix asphalt
SPL sound pressure level
TAC Technical Advisory Committee ( ADOT)
TLPA two layer porous asphalt
TxDOT Texas DOT
UK United Kingdom
UV ultra- violet
WIDOT Wisconsin DOT
1
Section 1
Introduction
Noise is one of the most pervasive forms of environmental pollution. It is everywhere and
affects our lives at home, work and play. By definition, noise is any unwanted or
excessive sound. It is an unwanted by- product of our modern way of life. While noise
emanates from many different sources, transportation noise is one of the most difficult
sources to avoid in society today. Highway traffic noise is a major contributor to
transportation noise.
Considering the impacts of traffic noise on members of the public, the Arizona
Department of Transportation ( ADOT), sought the services of a qualified firm or
individual to perform a survey of traffic noise reduction products, materials, and
technologies. Prophecy Consulting Group, LLC ( hereafter referred to as Project
Researcher) provided these services under Contract No. T0549A00028.
The Department provided the following objectives for the traffic noise reduction
study:
a. Identify noise reduction products, materials, and technologies currently available
and that have potential as noise mitigation alternatives.
b. Compile available performance information and discuss whether a full- scale
testing program by the department is recommended.
This report provides the results of this research study and recommends future work or
activities on this topic.
1.1 Scope of Work
A project approach was initially provided in the request for proposal ( RFP) document.
The Work Plan agreed upon by the Technical Advisory Committee ( TAC) and the
Project Researcher identified seven project tasks. :
Task 1: Develop Work Plan
A draft work plan was developed by the Project Researcher and distributed to members
of the TAC prior to a project meeting on March 18, 2005. Elements of the draft work
plan were discussed during this meeting.
The draft work plan was updated to include the recommended changes by the TAC
during the meeting and subsequent comments. The work plan was approved on April 5,
2005.
2
Task 2: Conduct Literature Review
A literature review was performed. Existing work in the field of noise reduction
products, materials, and technologies was reviewed. Research tools used included
technical journal indices and abstracts, other periodicals, newspapers, text books,
handbooks, directories, the internet, and technical societies.
The TAC recommended that the Project Researcher prioritize the research into three
areas of noise reduction approaches: Products, Technologies, and Materials. For each
relevant reference, the researcher was to document: the work that was done, the
organization that conducted the research, the date of the study, the research outcome or
findings, ease of implementation and associated costs.
Task 3: Survey Government and Non- government Organizations
Using the results of the literature review, a survey was developed and sent to government
and non- government agencies. To better meet the requirements of the task, a question on
the survey queried the organization on its expected future use of any noise reduction
product, material, and/ or technology.
The list of government and non- government agencies was developed by the Project
Researcher with input from the ADOT Project Manager. Contacted agencies were
encouraged to submit the survey by email.
Task 4: Assess Growth of Alternative Noise Reduction Products, Materials and
Technologies
An assessment of the expected growth in the acceptability and use of alternative noise
reduction products, materials, and technologies was made based on the findings in Tasks
2 and 3.
Task 5: Recommend Next Steps
Using the information obtained in Tasks 2 thru 4, the Project Researcher provided ADOT
with a list of recommended next steps for future work in the area of noise reduction
products, materials, and technologies. This list was developed by assessing available
performance data, scalability, and application of each proposed product, material or
technology. Arizona’s diverse climate, traffic, and roadway conditions were also
considered in the development of these recommendations.
Task 6: Submit Final Report
This document constitutes the Project Final Report. A separate four- page summary was
also prepared as a “ Research Note” for ADOT. The final report was prepared in
accordance with the ATRC document, “ Guidelines for Preparing ATRC Research
Reports, September 2003”.
3
Task 7: Make Oral Presentation to Research Council ( Optional)
If requested, the Project Researcher will make a presentation to ADOT’s Research
Council, or another group of stakeholders.
1.2 Report Organization
Section 1 – Introduction
Section 1 summarizes the scope of work for this research study, includes information on
noise control regulations at the federal, state, and local levels, and provides an outline of
the Project Final Report.
Section 2 – Literature Review
A summary of the literature on pavement noise reduction products, materials, and
technologies is provided in Section 2. The information and data presented is
representative of significant work that has or is being done in this area.
Section 3 – Survey Development
Section 3 provides information on the survey development and the process used to
identify and distribute it to potential respondents.
Section 4 – Survey Results
Results of the pavement noise reduction survey are summarized in Section 4.
Section 5 - Potential Growth of Pavement Noise Reduction Measures
Section 5 identifies those measures that are reasonably easy to implement and are most
likely to be used by ADOT and other transportation organizations in the near future based
on the findings of this research.
Section 6 – Conclusions and Recommendations
Conclusions of the research findings are provided in Section 6 along with
recommendations for future work or analysis on this topic.
A cross section of traffic noise reduction products identified in the literature survey is
provided in Appendix 3. No doubt this is not an exhaustive list but includes a wide array
of applications described in the literature.
4
5
Section 2
Literature Review
A review of the literature on pavement noise reducing products, materials, and
technologies was conducted to identify current and emerging methods and practices.
Findings from the literature review are reported by noise reduction category. The
references in this section highlight significant work done in the area.
2.1 Pavement Noise Reduction Products
For purposes of this study, a noise reduction product is considered an item that is readily
available on the market. The most commonly adopted noise reduction product that has
been used in the U. S. is noise walls. One of the attributes of a noise wall is that it has the
ability to reduce all noise coming from the roadway regardless of source.
Noise walls are built between the highway and the adjacent neighborhood. These
structures are expensive to build ( often $ 1 to $ 2 million per mile) and to maintain ( graffiti
is a major problem). In addition, sound waves can bend over and around objects, and
spread out with distance, therefore noise barriers may be limited in their usefulness to
distances of less than 400 m ( 436 yd) from the roadway. 1 Effective noise barriers can
reduce noise levels by 5 to 10 dB, cutting the loudness of traffic noise by as much as one
half. For example, a barrier that achieves a 10 dB reduction can reduce the sound level of
a typical tractor trailer pass- by to that of an automobile.
Barriers can be formed from earth mounds or " berms" along the road, from high vertical
walls, or from a combination of earth berms and walls. Earth berms have a very natural
appearance and are usually attractive. They also reduce noise by approximately 3 dB
more than vertical walls of the same height. However, earth berms can require large areas
of land to construct, especially if they are very tall. Walls require less space, but they are
usually limited to eight meters ( 25 feet) in height for structural and aesthetic reasons. 2
To effectively reduce the noise coming around its ends, a barrier should be at least eight
times as long as the distance from the home or receiver to the barrier. Noise barriers can
be constructed from earth, concrete, masonry, wood, metal, and other materials. To
effectively reduce sound transmission through the barrier, the material chosen must be
rigid and sufficiently dense ( at least 20 kg/ sq. m, or 36.9 lbs/ sq. ft). 3 All noise barrier
material types are equally effective, acoustically, if they have this density.
Two characteristics that distinguish one noise reduction product from another are the
Noise Reduction Coefficient ( NRC) and the Sound Transmission Class ( STC). 4 NRC is a
single- number index for rating how absorptive a particular material is. Although the
standard is often abused, it is simply the average of the mid- frequency sound absorption
coefficients ( 250, 500, 1000 and 2000 Hertz rounded to the nearest 5%). The NRC gives
6
no information as to how absorptive a material is in the low and high frequencies, nor
does it provide a relationship to the material’s barrier effect or STC.
STC is a single- number rating of the barrier effect of a material or assembly. Higher STC
values are more efficient for reducing sound transmission. For example, loud speech can
be understood fairly well through an STC 30 wall but should not be audible through an
STC 60 wall. The rating assesses the airborne sound transmission performance at a range
of frequencies from 125 to 4000 Hertz. This range is consistent with the frequency range
of speech. The STC rating does not assess low frequency sound transfer. Special
consideration must be given to spaces where the noise of concern is something other than
speech, such as mechanical equipment or music.
Even with a high STC rating, any penetration, air- gap, or “ flanking” path can seriously
degrade the isolation quality of a wall. Flanking paths are the means for sound to transfer
from one space to another other than through the wall. Sound can flank over, under, or
around a wall. Sound can also travel through common ductwork, plumbing or corridors.
There are no federal requirements specifying the materials to be used in the construction
of highway traffic noise barriers. 2 Individual State DOTs select the materials when
building these barriers. The selection is normally based in part on factors such as
aesthetics, durability, maintenance, cost, and the desires of the public.
2.1.1 Noise Wall Expenditure and Materials
For the year ending December 31, 2004, 45 State DOTs and the Commonwealth of
Puerto Rico constructed over 2,205 linear miles of sound barriers at a cost of over $ 3.4
billion in 2004 dollars. Five states ( Alabama, Mississippi, Montana, Rhode Island, and
South Dakota) and the District of Columbia did not construct noise barriers for the same
period. 3 Total noise barrier areas by material type are shown in Table 1, and a summary
of noise barrier data for the United States is provided in Table 2.
7
Table 1
Total Noise Barrier Area by Material Type ( through 2004) 3
Combination Barriers
Material
Square Feet
( Thousands)
Material Square Feet
( Thousands)
Concrete/ Precast 67,926 Wood/ Concrete 4,281
Block 33,993 Berm/ Wood 2,990
Concrete/ Unspecified 13,715 Concrete/ Block 2,154
Wood/ Post & Plank 5,912 Other 1,930
Berm Only 4,281 Berm/ Concrete 1,863
Metal/ Unspecified 4,279 Metal/ Concrete 1,786
Wood/ Glue Laminated 3,701 Berm/ Metal 1,439
Absorptive 3,629 Berm/ Block 795
Wood/ Unspecified 3,055 Concrete/ Brick 586
Other 1,812 Wood/ Metal 464
Brick 1,152 Berm/ Wood/ Concrete 348
Wood/ Block 283
Berm/ Wood/ Metal 171
Block/ Brick 8
Total 143,455 Total 19,098
Table 2
Noise Barrier Data for United States ( through 2004) 3
State
Square Feet ( Thousands)
State
Linear Miles
California 30,644 California 482.8
Virginia 11,227 Arizona 155.1
Arizona 11,226 Virginia 127.5
New Jersey 9,440 Ohio 112.4
Ohio 8,675 New Jersey 96.9
Maryland 8,422 Colorado 92.5
Minnesota 7,187 New York 90.7
New York 7,011 Pennsylvania 87.0
Florida 6,700 Minnesota 83.7
Pennsylvania 6,415 Maryland 81.8
10 State Total 106,946 1,410.4
Actual Cost ( Millions) 2004 Dollars Millions
California $ 399.6 California $ 592.8
Arizona 258.7 Arizona 284.6
New Jersey 202.4 New Jersey 277.5
Maryland 200.9 Maryland 253.6
Virginia 169.6 Virginia 225.3
New York 165.9 New York 207.3
Pennsylvania 159.6 Pennsylvania 197.8
Florida 150.7 Florida 175.9
Ohio 117.2 Ohio 139.0
Colorado 80.0 Minnesota 107.7
10 State Total $ 1,904.5 $ 2,461.4
Note: California did not supply barrier data for 1998- 2004.
8
2.1.2 Noise Wall Treatments and Coatings
Appendix 3 provides a sampling of traffic noise reduction products. While this is not an
exhaustive list, it does cover a wide array of potential applications found in the literature.
A recent concept in noise barrier design is the placement of sound absorptive materials on
top of barriers. Sound absorptive materials have been applied either on a large portion of
the surface area of the barrier, or at specific locations to reduce sound reflection off the
barrier surface. During the early 1970s, it was first proposed that lining the region in the
immediate vicinity of the edge of a barrier with sound absorptive material could result in
a potential reduction in sound pressure in the shadow zone. 5
Shadow zone is a term commonly used in oceanography or geology. Refraction produces
shadow zones that sound waves do not penetrate because of curvature. However, if the
object has a diameter greater than the acoustic wavelength, a “ sound shadow” is cast
behind the object where the sound is inaudible. ( Note: Some sound may be propagated
through the object depending on the material).
Acoustic treatments on the road side of barriers have been used to reduce the noise
reflected off the walls. The results of full scale experiments show that the performance of
a 2m ( 6.56ft) high barrier was reduced by 4 dBA when another reflective barrier of a
similar height was present on the other side of the road. 6 However, the researchers later
reported that the measured effects of applying absorptive materials to roadside barriers
are generally less than 1 dB on the A- weighted equivalent noise level, LAeq, and the A-weighted
noise level 10% of the time, LA10. Sound absorptive barrier tops or “ top
treatments” have been studied in theory as well as application with noise reductions
reported from 1 to 5 dBA. 6
The Institute for Safe, Quiet, and Durable Highways studied various shapes of sound
absorptive “ caps” and two alternative materials - glass fiber and polyolefin foam with
closed cells ( QUASH). This wall “ capping” concept was studied both in the laboratory
and on a section of sound barrier along US 20 in Elkhart County, Indiana. 7,8 Actual field
measurements showed that when the QUASH add- on device was attached to the existing
barrier edge, the benefit of the sound barrier increased between 2 dB and 5 dB at
frequencies from 2000 to 5000 Hz.
Although limited work has been done with barrier treatments, if an effective method
could be found, the possibility for greater noise reduction or deflection could be
significant in Arizona based on the amount of investment in noise barriers, and future
maintenance needs.
2.2 Noise Reduction Materials
The contribution to roadway noise created by tire- pavement interaction on the road
surface, pavement smoothness, and pavement texture is at issue here. In this subsection,
pavement noise reducing materials are defined as aggregate and other materials that are
9
applied to the surface as a part of the roadway design. As examples, these materials
include asphalt surfaces, portland cement concrete, sand and gravel.
Rubberized pavement, asphalt- rubber, and rubberized asphalt are often used
synonymously to describe a blend of asphalt cement, reclaimed tire rubber and certain
additives. The rubber component in this blend is at least 15% by weight of the total blend
and has reacted in the hot asphalt cement sufficiently to cause swelling of the rubber. 9
Interestingly, this non- proprietary, non- patented public process was developed in the
1960' s by a City of Phoenix engineer and has been routinely used in the U. S. by
transportation agencies in Arizona, California, Texas and Florida. The blend also has
been used on five continents. The higher binder content ( between 8 to 10%) allows for
more coating on the aggregate and produces a longer lasting pavement. Smoother ride
and noise reduction are two major benefits of asphalt- rubber hot mix pavements.
2.2.1 Pavement Treatments
The work done by European countries in using pavement surface type as a noise
reduction strategy has been well recognized and documented. Research by Kandhal10
shows that numerous studies were conducted in Europe in the 1980s and 1990s to
determine comparative noise levels of dense- grade hot mix asphalt ( HMA), open- graded
asphalt friction course ( OGFC), Portland cement concrete ( PCC) pavements, and stone
matrix asphalt ( SMA). The general conclusions drawn from these studies are provided in
Table 3.
Table 3: Noise From Different Pavement Surface Types ( International Studies) 10
Country/ Agency
( Year Reported)
Surface Type
Evaluated*
General Conclusions
British Columbia, Canada
( 1999)
HMA, OGFC After three years in service, the OGFC is quieter than the
HMA by 3.5 to 4.0 dBA.
Italy ( 1998) HMA, SMA As much as 7.0 dBA reduction in noise level has been reported
at 110 km/ h when SMA was compared to HMA
Germany ( 1991 and 1998) HMA, SMA SMA was 2.5 and 2.0 dBA quieter than HMA.
Nordic Countries ( 1994) HMA, OGFC A joint Nordic project determined OGFC to be quieter than
HMA by 3 to 5 dBA.
Belgium ( 1994) HMA, OGFC, PCC HMA was quieter than PCC ( old pavement) by 3.4 dBA,
OGFC was quieter than PCC by 7.5 dBA, OGFC was quieter
than transverse grooved PCC by 10.5 dBA.
World Road Association –
formerly PIARC ( 1993)
HMA, OGFC, PCC,
Chip Seal
The following ranges of noise levels have been reported in this
extensive report: OGFC 69- 77 dBA, HMA 72- 79.5 dBA, and
PCC 76- 85 dBA.
United Kingdom ( 1993) Rolled Asphalt,
OGFC, PCC
OGFC was quieter than rolled asphalt surface ( used in UK) by
4 decibels. OGFC was quieter than PCC by 6- 7 decibels.
Danish Road Institute
( 1992)
HMA, OGFC OGFC was quieter than HMA by 4 dBA.
Italy ( 1990) HMA, OGFC OGFC was quieter than HMA by 3 dBA
Germany ( 1990) HMA, OGFC OGFC was quieter than HMA by 4 to 5 dBA.
Sweden ( 1990) HMA, OGFC OGFC was quieter than HMA by 3.5 to 4.5 dBA.
France ( 1990) HMA, OGFC OGFC was quieter than HMA by 3 to 5 dBA.
Netherlands ( 1990) HMA, OGFC OGFC was quieter than HMA by about 3 dBA.
* HMA = dense- graded hot mix asphalt, OGFC = open- graded asphalt friction course, PCC = Portland cement concrete, SMA = stone matrix asphalt
1 0
Similarly, Khandal provides a summary of some noise level studies conducted in the U. S.
for pavement surfaces made of HMA, OGFC, PCC, and SMA in Table 4. Using dense-graded
HMA as the base reference, the average comparative noise levels for these
pavement surface materials are OGFC = - 4 dBA, SMA = - 2 dBA, HMA = 0 ( reference)
and PCC = + 3 dBA.
Table 4: Noise From Different Pavement Surface Types ( National Studies) 10
State Agency
( Year Reported)
Surface Type
Evaluated*
General Conclusions
Texas ( 2003) HMA, PCC An existing continuously reinforced concrete pavement ( CRCP) was
overlaid with asphalt- rubber OGFC. On average, the roadside noise
was reduced from 85 to 71 dBA. The reduction of 14 dBA is very
high and is possibly the largest noise reduction ever recorded on a
Texas DOT project.
California ( 2002) HMA, OGFC After four years in service on I- 80 near Davis, the OGFC is quieter
than the HMA by 4 to 6 dBA.
Michigan ( 2002) HMA, SMA, PCC A limited number of pavements were tested by close proximity
method. Considering the noise data obtained at 60 mph with an
aggressive tire pattern, the following noise levels were recorded in
dBA: SMA = 98.3, HMA = 98.9, and PCC = 98.9 to 100.8. For
PCC, the quietest surface was the diamond ground with 98.9 dBA,
which was about equal to HMA.
Michigan ( 2000,
2001)
HMA, OSMA,
PCC
The first study ( 2000) was conducted on I- 275, west of Detroit. It
indicated Superpave HMA was 4 to 5 dBA quieter than PCC. The
second study ( 2001) conducted on I- 94, west of Ann Arbor, showed
that a 12.5 mm SMA was approximately 4 dBA quieter than 12.5
mm Superpave HMA.
Wisconsin ( 1997) HMA, PCC The noise from HMA pavements was about 2 to 5 dBA less than
PCC pavements.
U. S. DOT ( 1995) HMA, OGFC, PCC Volpe National Transportation Center ( U. S. DOT) made numerous
noise measurements in multiple states to collect data for FHWA’s
noise model. For automobiles, PCC pavements were about 3 dBA
quieter than dense- graded HMA. OGFC was about 1.5 dBA quieter
than dense- graded HMA. ( Note: These OFGC data do not represent
European type new- generation OGFCs that are now used in the U. S.
and are significantly quieter.)
Minnesota ( 1995,
1987, and 1979)
HMA, OGFC, PCC OGFC was found to be quieter than HMA in the 1979 study. HMA
was found to be quieter than PCC in all three studies.
Oregon ( 1994) OGFC, PCC Compared to PCC pavements, the OGFC were 5.7 to 7.8 dBA
quieter.
Maryland ( 1994) HMA, SMA Average noise level of SMA was 1 dBA lower than HMA.
New Jersey ( 1994) HMA, SMA, PCC One PCC pavement and one HMA pavement were overlaid with
SMA. Noise levels were determined before and after the overlays.
Measurements during the afternoon rush hours showed SMA to be
quieter than PCC by 2.0 dBA before overlays.
Wisconsin ( 1993) HMA, SMA Similar to Maryland, the average noise level of SMA was 1 dBA
lower than HMA.
Maryland ( 1990) OGFC, PCC The OGFC was quieter by 2.3 to 3.6 dBA than the PCC pavement.
FHWA ( 1975) HMA, OGFC, PCC Noise level studies were conducted in Arizona, California, and
Nevada. Based on average dBA values, OGFC was quieter than
HMA by 2 dBA, and quieter than HMA by 2.1 dBA. The HMA
pavement was quieter than PCC by 2.0 dBA before overlays.
* HMA = dense- graded hot mix asphalt, OGFC = open- graded asphalt friction course, PCC = Portland cement concrete, SMA = stone
matrix asphalt
1 1
2.2.1.1 OGFC for Noise Reduction
The current rubberized asphalt that is being used in Europe and a few south- western
states is OGFC. 10 California DOT and Texas DOT ( TxDOT) have been actively involved
in quiet pavement studies utilizing OGFC. OGFC is referred to as porous friction course
( PFC) in Texas. TxDOT’s first PFC was placed in 1999. As of 2004, 25 additional PFC
projects had been completed. PFC mixtures have gained popularity as a paving material
due to their ability to reduce the risk of hydroplaning, reduce the amount of splash and
spray, reduce pavement noise, improve visibility of traffic striping in wet weather, and
improve ride quality. 11
Data reported in Table 4 for the State of California is the result of a three- year study to
determine if the noise attenuation benefits of OGFC decreased over time. A nine
kilometer ( 5.59 mile) portion of pavement on I- 80 near Davis, CA was repaved in June
1998. The new pavement cross section consisted of a 60 mm dense graded asphalt
concrete ( DGAC) leveling course that was overlaid with 25 mm ( 0.98 in) of OGFC.
Immediately after applying the DGAC base, roadside noise levels declined by 3 to 4 dBA
from baseline conditions. After application of the OGFC, roadside noise levels declined
by about 5 dBA from the baseline condition. Noise levels continued to be 4 to 6 dBA
lower than baseline condition over the entire study period. 11
Although OGFC provides a number of pavement noise reduction benefits, one of the
concerns reported at the SILVIA conference24 is that it is not porous, it is not pervious to
rainwater, and it does not perform well in colder climates. This is problematic for those
areas of Arizona at higher elevations and which experience colder winters than lower
elevation areas like metropolitan Phoenix and southern Arizona.
New generation OGFC ( NGOGFC) is also gaining popularity as a safe pavement,
especially for winter weather conditions. NGOGFC contains approximately 20 percent
more asphalt ( by volume) than conventional or first generation OGFC. NGOFC is
designed to have a minimum of 18 percent air voids. The design of conventional OGFC
did not focus on air voids. However, conventional OGFC mixtures typically contain
between 10 and 15 percent air voids. 11 At lower air voids percent levels moisture can get
trapped within the void matrix of the conventional OGFC. The void structure of
NGOGFC allows the mix to be more permeable and less likely to trap water.
A TxDOT report to their research management committee notes the following benefits of
NGOGFC:
• overall good friction and lower noise, in wet weather conditions - higher visibility
• reduced splash and spray
• reduced hydroplaning, and
• reduced night- time surface glare.
Also noted in the report are some of the common problems encountered with OGFC –
lack of durability ( raveling in 6 to 8 years), accumulation of frost and ice, and clogging of
pores. NGOGFC is also reported to be 22.5% more expensive than OGFC. 12
1 2
Transportation officials in The Netherlands have more than five years of experience with
second generation porous asphalt surface courses with rubberized asphalt binders,
ranging from test sections to large scale use. The new concept consists of a double-layered
porous asphalt construction, made up of a bottom layer of fine- graded porous
asphalt ( aggregate size 4 to 8 mm / 0.16 to 0.32in). The binder in both layers is
rubberized asphalt. The fine texture of the top layer causes a reduction of traffic noise,
from 3 to 4 dBA at 50 km/ h ( 31mph) up to 5.5 dBA at 100 km/ hr ( 62mph). 11
In 2005, the FHWA, American Association of State Highway Transportation Officials
( AASHTO), and the National Cooperative Research Highway Program ( NCRHP),
sponsored a scanning study of European quiet pavement systems. A cross- section team
of 14 state, federal, academic, and industry representatives visited five European
countries: Denmark, France, Italy, the Netherlands, and the United Kingdom ( UK). All
countries have policies that require the use of quiet pavement or other measures to reduce
traffic noise. Each country is also conducting research on quiet pavement technologies. 13
The focus of the tour was the three technologies below:
• Thin- surfaced, negatively textured gap- graded asphalt mixes ( e. g. Novachip,
micro- surfacing, and some SMA),
• Single- and double- layer highly porous asphalt mixes ( greater than 18% voids),
• Exposed aggregate concrete ( EAC) pavements.
The Danish government has experimented with both single- and double- layer porous
mixes and thin- layer mixes as pavement noise reducing strategies. The porous mixes
have the greatest potential to reduce noise by 3 to 5 dB, but have performance problems
with clogging and durability. Thin mixes are more cost- effective and appear to be more
durable. However, noise reduction achieved is lower at 1 to 3 dB. In some cases two-layer
OGFC or porous asphalt is being used as a noise- reducing strategy in place of
sound walls. Denmark requires porous mixtures to be at least 18 percent air voids. The
proposed system incorporates a large stone mix ( 16 or 22 mm / 0.62 or 0.86 in) in the
lower layer, and a smaller stone mix ( 5 or 8 mm / 0.20 or 0.31 in) in the upper layer. This
pavement system has added benefits in that it prevents the OGFC from clogging during
service. 10, 13
France employs the following techniques for pavement noise reduction: 13
• Use separate structural and surface characteristics,
• Use best- quality aggregates,
• Adjust pavement dressing to noise characteristics,
• Use smaller aggregate size for best adhesion ( skid resistance).
French transportation officials acknowledge the use of thicker surfacing ( 5 to 8 cm / 1.95
to 3.12 in) and continuous grading to ensure good waterproofing of the pavement.
However, very thin ( 2 to 3 cm / 0.78 to 1.17 in) and ultrathin ( 1.5 cm / 0.59 in) mixes
developed to improve the surface characteristics ( skid resistance, noise) are being used
today. The grading composition of mixes is 0 to 6 mm ( 0.23 in) and 0 to 10 mm ( 0.39 in)
gap graded. These surface mixes are usually 25 to 30 mm ( 0.98 to 1.17 in) thick with 5.7
1 3
to 5.9% asphalt. Gap grading appears to increase the raveling potential for these
pavements. The addition of 7 to 10% sand mortar has helped to resist raveling.
In the UK, plans are underway to resurface 60 % of the strategic road network with
quieter materials for a 10- year period ending in 2010.13 Transportation officials have
experimented with EAC finishes, but thin- layer quiet surfaces are now the paving
materials of choice because they are more cost effective, even on concrete pavements.
2.2.1.2 Concrete Treatment for Noise Reduction
Kansas DOT ( KDOT) rehabilitated eight miles of I- 435 with 3- inches of asphalt laid over
a 1- inch reflective cracking interlayer ( RCI). The interlayer was a polymer with a heavy
oil content – a modified emulsion as a tack coat between the two lifts. The finished HMA
overlay reduced the noise level from the original transverse tined PCC pavements by
about 7 dB. The National Center for Asphalt Technology ( NCAT) tested the pavement
surface for noise levels before and after the project. 14 Local residents described the noise
levels before and after the project as a “ difference between night and day”.
Similarly, Wisconsin DOT ( WIDOT) tested Italgrip, a very thin surface treatment
consisting of a two- part polymer resin, and found it to be a suitable and cost- effective
technique to enhance the safety and drainage characteristics of their roadways. The
Italgrip system is designed to improve the frictional characteristics of a pavement surface.
It is primarily intended for application in heavily trafficked short sections of roadway
with friction problems or high accident rates. 15 A 3 mm ( 0.12 in) Italgrip aggregate was
applied to both eastbound lanes, while a 4 mm ( 0.16 in) aggregate was applied to the
westbound lanes near I- 94.
The following steps were followed after diamond grinding of the roadway section:
• a two- part polymer adhesive was carefully applied to the pavement surface,
• the Italgrip aggregate was then back- spread over the polymer,
• after setting for a few hours, the surface was vacuum swept and re- opened to traffic.
The following outcomes were observed from the WIDOT study:
• grinding of the PCC pavement and application of the Italgrip resulted in no major
shift in frequency spectrum when comparing the tined PCC pavement, ground PCC
pavement and ground PCC pavement with Italgrip;
• a 3 dB decrease in the noise level due to diamond grinding, an additional 1 dB
reduction in noise level when the Italgrip is compared to the ground PCC pavement
at 96 km/ h and 104 km/ h ( 60 mph and 65 mph), and a 2 to 3 dB decrease in noise
level when the Italgrip is compared to the ground pavement between 1,550 and
2,000 Hz;
• a noticeable change in sound to the ear;
• no significant change in noise level at 112 km/ h ( 70 mph) between Italgrip and the
ground pavement;
• no significant noise level difference between the 3 mm and 4 mm ( 0.12 and 0.16
in) aggregate.
1 4
Prior to 1999, the Italgrip System had never been used in the United States. However, the
system had been in use in Italy for 10 years.
Although EAC pavements are commonly used in European countries, the technique has
not been routinely used in the United States. EAC pavements are normally constructed
using a two- layer “ wet on wet” paving process. The top layer thickness typically ranges
from 38 to 70 mm ( 1.5 to 2.75 in.). The mix contains fine siliceous sand and a high- qual-ity
coarse aggregate with an ideal maximum size of 6 to 12 mm ( 0.24 to 0.48 in.). Aggre-gates
used in the lower layer of the pavement can be of more modest durability and com-monly
include recycled materials that help reduce the overall cost of the concrete. Studies
have shown that the use of smaller aggregates provided better noise reduction levels. 16
The only large- scale EAC pavement project in the U. S. was completed in 1993 on
Interstate 75 in downtown Detroit, Michigan. The exposed aggregate concrete pavement
was comprised of a 254 mm ( 10 in.) jointed concrete pavement constructed in two lifts.
The top layer of the pavement was 64 mm ( 2.5 in.) thick with polish- resistant aggregates,
and the bottom layer was 191 mm ( 7.5 in.) thick with conventional aggregates. The lifts
were bound using a “ wet- on- wet” procedure. When compared to a conventional jointed
reinforced concrete pavement textured with transverse tines spaced 25 mm ( 1.0 in.) apart,
the section provided a reduction of only 0.4 dBA in exterior noise levels, although similar
European projects reported noise reductions between 4 and 5 dBA. 16
Researchers believe that the disappointing values may have resulted from too much
macrotexture on the exposed aggregate surface, combined with excessive spacing
between the coarse aggregate particles. This excessive spacing was a result of large sand
particles. Perhaps the difference in the U. S. and European experiences with EAC was a
motivating factor for the renewed interest in EAC pavements on the recent 2005 FHWA
scanning tour.
EAC pavements also exhibit properties associated with pavement texturing due to the
size of aggregates used and the texture depth of the stones. This material is also discussed
in Section 2.3, Pavement Noise Reduction Technologies.
Pervious or porous concrete is a material with large voids that are intentionally built into
the mix. The resulting permeability allows water ( and air) to flow readily through this
material. When used in highway applications, pervious concrete is typically used as a top
layer ( wearing course), providing both low noise emission and good drainage capacity.
The pervious concrete typically overlays a conventional ( dense) concrete pavement using
a “ wet- on- wet” process. Noise reduction in this composite system is a result of the
pervious material’s acoustical absorption, while strength and durability are improved by
the presence of the underlying concrete pavement layer. 16
Porosity levels for pervious concrete pavements typically range between 15% and 20%.
To attain good noise reduction characteristics, porosity should be at least 25%. Research
from Purdue University’s Institute of Safe, Quiet, and Durable Pavements has reported
that sound absorption levels were improved when higher porosity was used.
1 5
When pervious concrete pavement was first constructed in Belgium, it was found to
exhibit undesirable durability in freezing weather. Subsequently, polymer additives were
used along with higher cement content. The result was a significant improvement in the
service life. 13, 16 A policy that is currently being pursued in Japan is to replace all
pavements with pervious systems due to their safety and riding comfort. To change over
their existing concrete pavements to a pervious system, the preferred option is thin-bonded
pervious concrete overlays. 16 Laboratory simulation tests have demonstrated that
pervious concrete pavements can resist rutting and have a higher wear resistance to tire
chains than porous asphalt.
Since 1993, Japan’s Public Works Research Institute ( PWRI) has been developing a new
low- noise pavement that is referred to as “ Porous Elastic Road Surface” ( PERS).
Potential noise reduction levels in Equivalent Noise Level ( Leq) exceed 10 dBA. PWRI
has already solved several of the problems with PERS such as insufficient adhesion
between the pavement and the base course, low skid resistance, and poor fire resistance.
PERS was first constructed on Japan’s National Highway Route 46. However, noise
reduction levels measured in the field were less than expected due in part to the small size
of the construction area. The noise reduction levels measured at the site are lower than
those measured at the PWRI test facility. The noise reduction effect of PERS was found
in the 1/ 3- bandwidth frequency of 800 Hz and over. 17
In a separate study, pervious concrete pavements were evaluated in Japan with two
experimental concrete sections, 200 mm ( 7.9 in) in thickness. When compared to dense
asphalt pavements, they displayed noise reductions of 6 to 8 dBA for dry surfaces and 4
to 8 dBA for wet surfaces. This study was conducted with cars traveling at speeds from
40 to 75 km/ h ( 25 to 45 mph). For heavy trucks, noise reduction values were 4 to 8 dBA
and 2 to 3 dBA for dry and wet surfaces, respectively. 18
One disadvantage of using pervious concrete pavements is the clogging of the
pavement’s pores. The pores clog over time due to depositions in the voids of dirt and
dust from the road surroundings, from wear of the pavement itself, and from tires. 13, 16
2.3 Noise Reduction Technologies
For the purposes of this research study, a pavement noise technology may be a part of the
process, equipment, or machinery that is used to apply the paving material to the road
surface. It does not include paving materials.
2.3.1 Pavement Texturing
Pavement texturing can be designed and built into a pavement or placed upon hardened
concrete pavement by equipment. The National Concrete Pavement Technology Center at
Iowa State University ( ISU), FHWA, ACPA, and other organizations have partnered to
conduct a multi- part, seven- year Concrete Pavement Surface Characteristics Project. 16
Part 1, Task 2, of the ISU- FHWA project, addressed the noise issue by evaluating
conventional and innovative concrete pavement noise reduction methods in Europe and
the U. S.
1 6
In the U. S., conventional concrete pavement surface options for controlling tire- pavement
noise fall into two categories: 16
• Conventional texturing ( performed while concrete is still in a plastic state)
o Drag textures ( including artificial turf and burlap drag)
o Tined textures ( including transverse and longitudinal)
• Diamond grinding ( performed on hardened concrete pavement)
A brief definition is provided for each category along with examples and outcomes of
field studies or applications that relate to pavement noise reduction. A summary of the
pavement texture options presented in this subsection is provided in Table 5 on page 23.
2.3.1.1 Drag Texturing
Broomed surface textures are created by dragging a handheld or mechanical broom along
the surface of the pavement, creating a ridged surface. This texture typically consists of
1.5 to 3mm deep ( 0.06 to 0.12 in.) grooves, either longitudinal or transverse to the
centerline of the roadway.
Artificial turf drag surfaces are similarly created by dragging an inverted section of
artificial turf along the surface of the pavement. This technique often employs a device
that controls the time and rate of texturing, most commonly a construction bridge that
spans the pavement. Grooves of 1.5 to 3 mm ( 0.06 to 0.12 in.) in depth are typically
created. Burlap drag ( also known as Hessian drag) texturing is created by dragging
moistened, coarse burlap across the surface of the pavement, typically creating grooves
with depths between 1.5 and 3 mm ( 0.06 and 0.12 in.).
Studies have shown that dragged textures are sufficient for roadways with speeds below
72 km/ h ( 45 mph). More recent pavement evaluations in Minnesota have concluded that
the use of drag texturing results in comparable noise levels and surface friction to
conventional HMA pavements. The required texture depth specification in Minnesota is
reported to be 1.0 mm ( 0.04 in.) 16
According to Cackler et al., 16 the majority of concrete highway systems in Germany are
finished using a burlap drag texture. The burlap drag finish provides adequate friction and
minimizes air pumping. However, the frictional characteristics of the pavements often
decrease due to pavement wear. Use of larger sand particles may increase the texture life
by up to six years. The larger sand on the other hand may also reduce the concrete’s
workability.
Drag texturing techniques may provide a less costly and often quieter pavement than
other alternatives. Measures should be taken to ensure adequate friction, both initially and
during the service life. This can be achieved by selecting materials and mixes with
improved wear resistance.
1 7
2.3.1.2 Tined Texturing
Transverse tining is the most common texture on high- speed road and highway
pavements in North America. 19 It is produced by a mechanical device equipped with a
tining head ( metal rake) that moves laterally across the width of the paved surface. For
smaller areas, a hand rake is often used. Optimal dimensions vary from 10 to 40 mm ( 0.4
to 1.6in) spacing for random tines with no more than 50% above 25 mm ( 1.0in), 3 to 6
mm ( 0.12 to 0.24in) tine depth, and 3 mm ( 0.12in) tine width. 14,19 Skewing of tines has
been found to reduce tire- pavement interaction noise.
Favorable friction qualities of transverse tining are particularly pronounced in wet
weather conditions. Deep macrotexture is capable of reducing the water film thickness
resulting in reduced potential for hydroplaning. Depending on the properties of the
concrete mixture, transverse tining can provide beneficial frictional qualities over the life
of the pavement.
Transverse tining has also been known to exhibit undesirable noise emissions due to the
interaction between the pavement and vehicle tires. Noise emissions from transverse
tined textures depend on tine spacing, depth, and width. A study conducted by WIDOT in
2000 concluded that wider and deeper transverse tine textures often produce greater
noise. 15,16
A 1977 Minnesota DOT ( MDOT) report to the state legislature discussed the testing of
different anti- skid groove spacings on PCC pavement. By changing the spacing from 1.5
to 1.0 inch, roadside noise levels were reduced 2.5 to 4.0 dB. 20 Using results from a
Wisconsin study, MDOT was able to reduce its spacing to 0.75 inch achieving a further
reduction of 1.5 to 3.5 dB and an overall reduction of 4.0 to 7.5 dB. Wisconsin and
Minnesota also conducted noise studies on different types of bituminous pavements that
resulted in even greater noise reductions. Although no details are available about the data
collection process or the data analysis, it is assumed that transverse tining was the
texturing process applied to the PCC pavement in this study.
Uniform transverse tine spacings typically range from 12.5 to 25 mm ( 0.5 to 1 in).
“ Wheel whine” is often associated with uniformly spaced tines. While the dBA level of a
tined surface may not necessarily be higher than other texturing methods, the tonal nature
of the whine makes this pavement texture objectionable to many. To help mitigate the
tonal qualities, random tining is recommended. A broad range of random tine spacings,
between 10 to 76 mm ( 0.4 to 3 in.) has been reported to reduce noise emissions. In
situations where concrete finishing conditions are unfavorable ( e. g., objectionable
weather conditions and lack of equipment control), random spacings of 10 to 51 mm ( 0.4
to 2 in.) are recommended. The FHWA has recommended two random tining patterns,
averaging 13 mm and 26 mm ( 0.52 in. and 1.04 in.), respectively. 16 The shorter spacings
have been recommended to mitigate the high noise levels reported by some states that
have tried or adopted random spacings.
1 8
Skewing of transverse tining involves forming the grooves at an angle, rather than
perpendicular to the centerline. This is a complementary method that has demonstrated
benefits related to tire- pavement noise while providing the friction commonly associated
with transverse tined pavements. Research by Cackler et. al. identified a skew with a
recommended longitudinal- to- transverse ratio of 1: 6.16
Longitudinally tined textures are constructed in a manner similar to that of transverse
tining, except that the tining device is moved longitudinally along the direction of paving.
Although longitudinal tining is not used as frequently as transverse, it has been used
extensively in some states, including California.
Longitudinal tining is commonly reported to exhibit lower noise characteristics thereby
increasing its popularity and use. However, some transportation agencies have been
cautious to use this texturing technique because the data shows longitudinally tined
surfaces to have lower friction numbers when compared to transversely tined pavements,
all else being equal. One possible explanation of this may be the shape of the grooves
with respect to the traction forces of the tire ( compared to transverse tining). It should be
noted, however, that longitudinal tining on horizontal curves has been shown to prevent
vehicle skidding and thus improve safety. 16 Some DOTs report that if adequate cross-slope
exists, the differences between the surface drainage on transverse and longitudinal
tining are minimal.
Research shows that the long- term effectiveness of longitudinally tined surfaces is
impacted by the design of the pavement mix. Data have shown that longitudinally tined
pavements should contain a minimum of 25% siliceous sand to improve the level and
durability of the friction capacity.
The WIDOT study further concluded that among all of the concrete pavements evaluated,
those with longitudinal tining provided “ the lowest exterior noise while still providing
adequate texture”. When the texture is properly designed and constructed, longitudinally
tined pavements can achieve friction characteristics and durability comparable to either
transversely tined concrete pavements or dense- graded HMA pavements. 16
Volpe assisted California DOT in a comparison of three PCC test sections: longitudinal
tining, burlap dragged, and broomed tining. Volpe also assisted ADOT in comparing
uniform longitudinal tining, uniform transverse tining, and randomly spaced transverse
tining. Their findings showed that the quietest surface treatments were CA burlap
dragged, CA broomed, and AZ uniform longitudinal tining. 11
2.3.1.3 Diamond Grinding
Diamond grinding is a technique that removes a thin layer of hardened concrete
pavement using closely spaced diamond saw blades. The diamond saw blades are stacked
side- by- side and generally remove between 3 and 20 mm ( 0.12 and 0.8 in) from the
surface. The blades are gang- mounted on a cutting head and can generate 164 to 197
grooves/ m ( 50 to 60 grooves/ ft). Although diamond grinding has traditionally been used
to rehabilitate existing pavements by restoring smoothness, it has also been found to
1 9
reduce tire- pavement noise and restore pavement friction. The grinding procedure results
in the development of macrotexture. Furthermore, directional stability is more easily
controlled, making diamond grinding more appealing to drivers than longitudinal tining.
In one study conducted to compare transverse tining to longitudinal diamond- grinding,
test sections were constructed and evaluated for safety, noise, and other pavement
characteristics. 20 Diamond grinding was used to remove a thin layer of the concrete
surface. In some cases, thin fins of concrete were left behind and were subsequently
broken off by a blade. Each grinding head consisted of 166 saw blades, 3.18 mm ( 0.125
in.) separated by spacers with a thickness of 2.67 mm ( 0.105 in).
It has been reported that the key variables of diamond grinding are cutting blades, cut
depth, equipment horsepower, and the properties ( e. g., hardness) of the aggregates used.
In a 2001 study by Burgé, Travis, and Rado, the grinding rate was approximately 0.6
lane- km ( 0.4 lane- mi.) per day In addition, there was a specified minimum curing time of
seven days before grinding. KDOT conducted a study in 2004 and concluded that smaller
blade spacings led to reduced noise levels. 16
The study concluded that the longitudinal ground pavement was quieter than the
transversely tined pavement by 2 to 5 dBA ( measured on the side of the road). 16 When
noise measurements were conducted a year later, there was no real change in noise levels.
When comparing different vehicle types, the ground surface led to a 5- dBA noise
improvement for light trucks and automobiles, and a 2- dBA improvement for medium
and heavy trucks. The lower noise reduction for larger vehicles is believed to be due to
differences in the noise emission source; larger vehicles generate a greater percentage of
noise from the engine and exhaust systems ( as compared to tire- pavement noise
emissions). 16 Prior to making a decision on a pavement surface technology, the
percentage of heavy vehicles should be considered in determining overall effectiveness of
surface treatments.
Several states, including Arizona, California, New Jersey, North Dakota, and Virginia
have experience with tined and textured surfaces of PCC pavements in addressing
roadway noise. A partnership has been formed between California and the Western
States- ACPA on the I- 280 pavement rehabilitation project in San Mateo County. Noise
from old longitudinally tined pavement will be compared to noise from a PCC pavement
with diamond grinding, a PCC pavement with texture grinding, and a PCC pavement
overlain with 30 mm ( 1.17 in) of OGFC. 20 Noise measurements will be made for three to
five years to assess the longevity of noise reduction benefits.
The 2005 European scanning team recommended investigating and optimizing diamond-grinding
blade configurations to enhance the noise- reducing properties of existing
concrete surfaces in noise- sensitive locations. To achieve noise reduction texture should
always be negative ( pavement depressions). Positively textured pavements, such as chip
seals, increase noise. Positive texture is the magnitude of texture that exists above a
planar surface ( the riding surface). Positive texture almost always produces greater noise
with increasing texture depth. Chippings on concrete or exposed aggregate surfaces
could be considered the extreme case of positive texture.
2 0
Negative texture refers to the magnitude of the texture that exists below a planar surface.
A longitudinally grooved pavement would represent a negative texture. Negative textures
do not “ interfere” with the tire, resulting in less vibration and noise than a positive
texture. Therefore, the effect of negative texture is different from the effect of positive
texture. 21 This is another reason why texture depth alone cannot be used to correlate
noise across different pavement types.
2.3.1.4 Exposed Aggregate Concrete ( EAC)
EAC was discussed in the previous section as a concrete pavement treatment that is
usually applied using a two- layer “ wet on wet” paving process. It is the combination of
aggregates used in the top layer that determine its surface characteristics and texture.
Texture depths, curing solutions, and concrete finishing techniques are used to determine
the best combinations for optimal performance.
During the 2005 FHWA scanning tour, UK transportation officials reported that they
experimented with EAC finishes and found thin- layer quiet surfacings to be more cost
effective. Belgium uses EAC pavements and SMAs. Both have been optimized for noise.
The porous surfaces provide a slightly better noise benefit than SMA and EAC, but
officials believe that the latter provides a better blend of durability and noise reduction.
The Dutch province of Noord- Brabant conducted a study intended to further determine
the surface characteristics of EAC pavements. Various aggregates, texture depths, curing
solutions, and concrete finishing techniques were used in the study to determine the
combinations that provided optimal performance. Two Dutch aggregates, Dutch stone
and Graukwartsiet, were used in the study. The Graukwartsiet possessed a higher
polished stone value than the Dutch stone aggregate. Several texture depths were
evaluated. The standard depth was considered to be one- quarter of the maximum
aggregate size. Different retarding agents were evaluated, including lemon, acid
solutions, and various combinations of retarding agents and curing compounds. One- and
two- layer paving systems, as well as a super smoother ( finisher) were also evaluated in
the study. 16
Several key measurements and observations were made after construction. Texture depth
was found to be affected by the use of a super smoother, which resulted in a maximum
texture depth of 1.8 mm ( 0.07 in). When not used, texture depths were not as great, with
values commonly between 1.1 and 1.6 mm ( 0.04 and 0.06 in). The super smoother was
shown to produce positive effects in regards to noise emission, possibly due to a
reduction in megatexture. The selection of the retarding agent did not appear to make a
difference on the results. It was concluded that lower noise levels were measured when
smaller maximum aggregates were used.
A Swedish Study tested several concrete and HMA pavements for abrasion resistance,
friction, and noise under heavy traffic. The test sections were constructed with exposed
aggregates in the surface on both jointed plain and continuously reinforced concrete
pavements. Two different maximum aggregate sizes were used in the design of the
2 1
concrete pavements, 8 and 16 mm ( 0.31 and 0.63 in). Noise was measured using the close
proximity ( CPX) method. In comparison to the HMA pavements constructed on the same
job, initial tests revealed that the EAC pavements with 16 mm ( 0.63 in) and 8 mm ( 0.31
in) stones provided noise levels that were 1.0 to 1.5 dBA and 3.0 to 3.5 dBA lower. 16
The noise emissions of the 16 mm ( 0.63 in) EAC and HMA sections were found to be
identical after one year. However, the 8 mm ( 0.31 in) EAC section actually produced
quieter noise levels after a year. Three years after construction, the noise levels from all
of the pavements had deteriorated. Also of interest was that during the winter season
concrete pavements produced noise levels about 1 dBA higher than the HMA pavements.
2.3.1.5 Pervious Concrete Pavements
Pervious concrete pavement was also discussed in the previous subsection as a pavement
treatment. A relationship between sound absorption and aggregate size was identified in
the research. In one study, a pavement with decreased aggregate size exhibited improved
sound absorption. A combination of # 4 and # 8 aggregates in the mixture exhibited
improved acoustic absorption characteristics when compared to straight gap grading. A
Belgian study reported sound reduction using pervious concrete as well, with a 5 dBA
decrease using a pervious concrete pavement with only 19% porosity. 16
Durability is commonly regulated by the interface of the two concrete layers and the
presence of pores. Once ice forms at the entrance of small pores and water is unable to
move, damage occurs very quickly. In pervious concrete, freezing tends to originate at
the top of the pavement and infiltrate into the lower depths of the layer. Differences in the
properties of the pervious and dense concretes can lead to stress concentrations at the
interface. The damage may take the form of an adhesion loss between the pervious
concrete and the conventional concrete. To combat this problem, continuous
maintenance and cleaning can be conducted to help preserve and restore the pavement’s
acoustical performance.
Double- layer pervious concrete has also been demonstrated as a possible solution where a
top lift with smaller aggregates is placed over a larger stone mix. The resulting system
may help to minimize infiltration of debris that causes clogging. The added cost of
constructing pervious concrete pavement must be taken into consideration. The long- term
effectiveness of this technique is still under debate. In one report by the Belgian Road
Research Centre it is noted that compared with a conventional concrete 22 cm ( 8.7 in)
thick a 4 cm ( 1.6 in) pervious concrete laid over 18 cm ( 7 in) of conventional concrete
has associated extra costs estimated at 40%”. However, no significant cost difference
was found with an equivalent structure including porous asphalt. The cost of constructing
quiet pervious concrete pavements in New Zealand has been reported at US $ 132 per m ²
( US $ 111 per sq. yd.). In the United States, pervious concrete projects have been reported
to cost 40% more. 16
2 2
2.3.1.6 Innovative Pavement Texturing Solutions
In his research on concrete pavement noise reduction methods, Cackler identified several
innovative texturing solutions that were either being researched or were in experimental
stage. 16
• Stamping, Brushing, and Other Texturing Techniques: Other proposed
alternative texturing techniques are proposed to conventional tining, but will
be designed with better surface characteristic properties.
• Sprinkle Treatment: This technique is similar to EAC and distributes partially
embedded, small, polish- resistant stone chips on fresh concrete surface. This
technique was previously used in the U. S. in the 1970s and 1980s; however,
the equipment was rented from England, and therefore not available for wide-spread
application. Equipment will need to be developed or purchased.
• Shot Peening ( or shotblasting): Special equipment is used to propel tiny steel
shots onto the pavement surface. The shots make an imprint on the surface
and remove a thin layer of mortar and aggregate, exposing coarse aggregate.
An open porous surface texture is created increasing skid resistance and
reducing noise levels.
• Use of Helmholtz Resonators: Originally developed at the University of
Göttingen in Germany, euphonic pavements were designed as “ quiet tire/ road
combination” pavements, incorporating “ Helmholtz resonators underneath a
perforated but planed aluminum structure”. Helmholtz resonators are designed
to absorb low frequencies, typically ranging between 100 to 250 Hz.
Other potential texturing techniques identified by Cackler include: 16
• Paving concrete that possesses inclusions ( e. g., fiberglass, foam, and rubber particles)
to increase acoustical absorption,
• Application of acoustically absorptive materials for concrete shoulders ( as opposed to
traffic lanes), allowing for noise of all sources to be absorbed en route to the receiver
and also reducing surface wear and clogging issues,
• Quiet joint designs, addressing the significant factor of wheel “ slapping” at the joints
in overall noise levels,
• Dimpling, waffling, or other innovative geometries of fresh concrete texture,
• Textured profile pans, e. g. a corduroy pattern, for example, might be machined into
the profile pan of a slip- form paver to construct a surface similar to that resulting
from diamond grinding.
2 3
Table 5: Summary of Concrete Pavement Texture Options16
Texture Description Current Use and Perception
Artificial turf
drag
Produced by dragging an inverted section
of artificial turf from a device that allows
control time and rate of texturing. Usually
a construction bridge that spans the
pavement typically produces 1/ 16 to 1/ 8
inch deep striations.
Artificial turf drag textures have shown sufficient friction
characteristics for many roadways, as well as reduced noise
relative to many transversely tined pavements. Minnesota has
used this type of texturing to reduce noise on high- speed roads.
Burlap drag Produced by dragging moistened coarse
burlap from a device that allows control of
the time and rate of texturing, usually a
construction bridge that spans the
pavement; typically produces 1/ 16 to 1/ 8
inch deep striations.
Burlap drag textures provide sufficient friction characteristics for
many roadways, especially those with speeds less than 45 mph,
and reduced noise relative to many transversely tined pavements.
This texture is used on Germany’s high- speed Autobahn system.
Transverse
tining
Produced by moving a mechanical device
equipped with a tining head across the
width of the paving surface laterally or on
a skew. Consistent concrete mixture and
constant forward movement of the paving
train at a uniform speed is required for a
consistent tining depth.
For tined pavements, texture depth and groove width are
important parameters in tire- pavement noise generation.
Pavements with uniformly spaced transverse tining generally,
but not always, exhibit undesirable “ wheel whine” noise.
Artificial turf or burlap drag texture precedes many projects.
Longitudinal
tining
Achieved by a mechanical device equipped
with a tining head ( metal rake) pulled in a
line parallel to the pavement centerline. For
consistent tining depth, maintain a
consistent concrete mixture and move the
paving train forward constantly at a
uniform rate of speed. Most projects
precede with an artificial turf or burlap
drag texture.
Tined texture depth and groove width are important parameters
in tire- pavement noise generation. Longitudinal tining is often
quieter than transverse tining. Narrower time spacings might be
used to reduce vehicle tracking and possibly reduce noise even
further. Lateral stability of narrow- tired vehicles may also
benefit from this.
Diamond
grinding
Longitudinal, corduroy- like texture made
by equipment using diamond saw blades
gang- mounted on a cutting head. About 50
to 60 grooves/ ft. are produced by the
cutting head 1/ 8 to ¾ inch is removed from
the pavement surface.
Diamond grinding has traditionally been used to restore
pavement smoothness, but has also been shown to reduce tire-pavement
noise and improve friction in the short term. Diamond
ground pavements do not affect vehicle tracking as much as
widely spaced longitudinally tined pavements.
EAC
pavement
European practice includes applying a set
retarder to the new concrete pavement and
then brushing or washing away mortar to
expose durable aggregates. Other
techniques involve the uniform application
of aggregates to the fresh concrete.
Regarded as an effective method for reducing tire- pavement
noise while providing adequate friction. Smaller aggregate sizes
have been reported to provide larger noise reductions, while
aggregates with a high polished stone value increase durability.
Only one large- scale EAC pavement project has been completed
in U. S.
Pervious
concrete
pavement
When used in highway applications,
pervious concrete is typically used as a top
layer ( wearing course), providing both low
noise emission and good drainage capacity.
The pervious concrete typically overlays a
conventional ( dense) concrete pavement
using a “ wet- on- wet” process.
Sound absorption increases with higher porosity levels for
pervious concrete, and also results from smaller aggregate sizes.
Use of pervious pavements for high- volume, high- speed
facilities is still in its infancy and will require more testing.
Regular maintenance and cleaning may be needed to prevent
clogged pores and to preserve the pavement’s acoustical
performance. Research on durability is ongoing in wet, hard-freeze
areas.
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2.3.2 Other Innovative Pavement Solutions
Traditionally, two- layer porous asphalt is laid in two passes – one pass per porous layer.
As a part of a Noise Innovation Program, equipment will be tested in the Netherlands to
construct two- layer porous asphalt in one pass – both layers being laid at the same time. 26
This technique is already in use in Germany with thin top layers. The objective of the
research is to determine if the “ one- pass placement” will increase the performance of the
two- layer pavement materials.
As a part of its Road to the Future program, 22 transportation researchers in the
Netherlands are focusing on long- term effects and the placement of pavement materials
using innovative and/ or fast construction techniques. Six experimental test sections have
been constructed:
a. The Very Silent Sound Module – this design has a functionally and physically
modular system. The sound- reducing functional modules contain Helmholtz
resonators. The road surface on top of the sound- reducing resonators is made of a thin
porous top layer. This single layer of asphalt has optimized surface properties, such as
low sound generation and a high skid resistance.
b. The Way of No Resound – this road design has three layers. Two top layers with a
combined thickness of 30 mm ( 1.2 in), are assembled in the factory as one roll- up
layer. The bottom layer is made up of concrete elements with a high supporting
power in which cavities that function as Helmholtz resonators are included. The pre-fabrication
of the top layer promotes a pavement surface without irregularities in the
macro- texture. This results in reduced vibration of a vehicle’s tires.
c. The Bonding Road – this design has a prefabricated asphalt mat on a roll that can be
bonded to or removed from the substrate very quickly by utilizing an “ on- off switch-ing”
bonding system. Prefabrication of the paving materials ensures a consistent high
quality end product. The bonding between the asphalt mat and the substrate can be
switched on or off by electromagnetic waves without any physical contact.
d. ModieSlab – the top layer of this road design consists of a 15 mm ( 0.6 in) open con-crete
layer, followed by another open concrete layer with coarsely broken gravel that
is 35 to 55 mm ( 1.4 to 2.2 in) thick. The thickness of the lower layer decreases from
the right to left lanes. Sound absorption is expected to match the type of lane traffic.
e. Quiet Transport – this road surface has porous asphalt with a very silent top layer.
During construction a special layer is installed to absorb engine noise. The pavement
design objective is to absorb both truck engine and tire noise.
f. Tapis Tolerance – the road construction for this pavement design includes a soft top
layer, a perforated compression layer, and an absorption layer of honeycomb profiles
in mineral wool. Due to the number of noise reducing elements, the expected noise
reduction potential is high, and more than likely the cost of road construction will
increase.
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Initial results for the pavement types tested under the Road to the Futures program are
shown in Table 6. These results reflect light vehicle traffic at 100 km/ h ( 62 mph). The
initial noise reduction levels reported for all pavement techniques vary between 5 and 7
dBA. The claimed reductions for some of the pavement techniques exceeded 10 dBA.
However, optimization of new pavement techniques may produce higher reduction levels.
Table 6: Initial Noise Reduction Levels for Light Vehicles
Road to the Future Project22
Pavement Technique Noise Reduction, dBA
Very Silent Noise Module 5
The Way of No Resound 6
The Bonding Road 6
ModieSlab 6 to 7
Quiet Transport 5 to 7
Tapis Tollerance 7 to 8
The 2005 FHWA Scanning Team noted the use of a single two- lift paver by Wirtgen
during their visit to Belgium. The Wirtgen paver allows for the use of lower- quality
aggregates in the base while using higher quality aggregates on the top surface. 13, 16,23
The two- lift process is not new to the U. S. and has been around almost as long as
concrete pavement. The two- lift paving technique was implemented extensively from
1950 to 1990 in many states to facilitate the placement of mesh in concrete during
interstate pavement construction. This pavement consisted of two layers placed wet on
wet, with the top layer consisting of a special surface mix. Beginning in the 1970’ s the
concrete paving industry moved away from a mesh dowelled design to a plain pavement
design, and shortening panels eliminated the need to pave with a two- lift process. Today
there are still some rare instances where the two- lift process is used in airport
construction to facilitate the placement of mesh between dowel baskets.
The two- lift process is used in Europe to develop a strong base pavement and a superior,
but thin, wearing surface. In France, continuous reinforced concrete pavement was
placed on two traffic lanes of highway A71 using the two- lift paving method. 23 The top
layer of this pavement, approximately 2 inches in depth, was made up of harder
aggregates. These aggregates provided low noise and high friction for the pavement
surface.
In Austria, the aggregate is secured with cement and then a two- inch layer of asphalt is
placed on top. The recycled aggregate is then mixed into the bottom 8.5 in deep concrete
layer, while the top 1.6 in deep layer was composed of a harder, higher quality
aggregate. The purpose of using a higher quality concrete for the top layer was to reduce
noise and increase friction, while keeping cost low by using a lower quality concrete for
the bottom layer. The case is very similar in Germany. Two- lift paving is often used to
reduce noise and increase friction. Germany also uses this method to reduce cost and
achieve a smoother profile. In addition, Germany has somewhat drastic climate changes,
which require the use of higher quality aggregate in the top layer to resist freezing and
thawing effects. 23
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The renewed interest in the two- lift process appears to be growing in the U. S.
Implementation of a two- lift system could help some agencies around the country
consume growing recycled asphalt piles, since most asphalt specifications only allow up
to 40% recycled asphalt in their product and generally only on the lower sections. If
recycled asphalt is available, it could be used to reduce costs as less of the more
expensive aggregates would need to be imported.
2.4 Other Considerations for Noise Source Reduction
Some methodologies that are being considered for pavement noise reduction do not fit in
any one of the three categories of interest identified in this study. Examples of such
methodologies include; developing a better understanding of the pavement attributes that
reduce noise generation for different vehicle types, evaluating pavement performance
with age, developing maintenance techniques that preserve the noise reducing
characteristics of pavement, and developing quieter tires without compromising safety.
At the InterNoise 2003 Conference, 22 transportation officials from The Netherlands
reported developing several projects under the Noise Innovation Program ( IPG) that
focused on the use of silent roads, improvement of tires and vehicles, optimization of
barriers, knowledge management, and facilities assessment methods. Their total budget
for noise abatement of road traffic is about 50 million euro. Looking to the future, one of
the keys to noise reduction from tire- pavement interaction on roadways in Arizona may
be the ability to model the effectiveness of combining several measures for a particular
application.
Sandberg identifies seven noise influencing road surface parameters ( Table 7) in an
international presentation to SILVA. 24 More interestingly, he notes that European
pavements are designed to be quiet, whereas California and Arizona pavements are off-the-
shelf.
Table 7: Noise Influencing Road Surface Parameters24
No. Parameter Degree of Influence
1 Macrotexture Very high
2 Megatexture High
3 Microtexture Low- moderate
4 Unevenness Minor
5 Porosity Very high
6 Thickness of layer High, for porous surfaces
7 Adhesion ( normal) Low/ moderate
8 Friction ( tangent.) See microtexture
9 Stiffness Uncertain (?), moderate
A significant finding reported by the 2005 FHWA Scanning Team is that the source level
of quiet pavements is being incorporated into existing highway noise prediction models
using varying methods. This effort falls under the Harmonised, Accurate, and Reliable
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Prediction Methods for the EU Directive on the Assessment and Management of
Environmental Noise ( HARMONOISE). The common EU model being developed will
incorporate pavement type in the prediction, along with other advanced prediction
parameters such as meteorological effects. 13 Pavement noise reductions of as little as 2
dB are being used in integrated noise strategies.
Under the European Union’s Environmental Noise Directive, adopted June 25, 2002, all
member countries are to:
a. Determine exposure to environmental noise through noise mapping,
including rural areas.
b. Use uniform prediction methods of assessment common to the members.
c. Ensure that information on environmental noise is made available to the
public.
d. Adopt action plans based on noise mapping results with a view toward
preventing and reducing environmental noise.
All member countries were to complete strategic noise maps and adopt actions plans on
or before June 30, 2007.
Many European highway paving projects are bid based on performance specifications.
The selection process is based on best- value contracting methods. Pavement vendors
have responded to agency performance criteria with innovative solutions that often carry
unequal risk, but if effective, can be held as proprietary for future project applications.
There appears to be large disagreement within the EU regarding effective maintenance of
negatively textured and highly porous pavements. Some countries require pressure
washing and vacuuming of the pavement at least twice a year, while others consider these
practices useless, or even harmful. Some countries have stopped using highly porous
pavements in snow and ice regions, and instead use SMA pavements with small
aggregate.
In the area or pavement noise research, an extensive amount of research on quiet
pavement technology is underway in the European Union and appears to be embedded in
the culture of the organizations. A research partnership exists between the transportation
agency and industry, and even with private entities. As an example, under the SIRIUS
program, companies are encouraged to submit innovative ideas that are judged by a panel
of topical experts. The best ideas are constructed as experimental sections. The selected
projects are highly sought after by companies as a marketing tool.
One of the recommendations from the 2005 scanning tour for US transportation
organizations was to consider reducing the aggregate size in the wearing surface of the
pavement to realize an immediate improvement in the noise- reducing properties of mixes.
In Europe, the aggregate sizes for quiet surfacing mixes are 4 to10 mm ( 0.16 to 0.4 in).
Most State DOTs use the Superpave aggregate gradings of 19, 12.5, or 9.5 mm ( 0.76, 0.5,
or 0.38 in). A drop in routine aggregate mix size to the next smallest gradation is
recommended and should produce a noise reduction of 1 to 3 dB. 13
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The emerging trend is to use thin- textured, gap- graded mixes with small aggregate in
urban or low- speed areas or areas subject to severe winter snow and ice accumulation.
The highly porous mixes are recommended for rural and high- speed roads with moderate
winter conditions. The European experience demonstrates that porous mixes are effective
in reducing noise when used properly. Early evaluation results in Europe indicate that
two- layer porous asphalt ( TLPA) appears to have potential application on high- speed
roads and produces exceptionally quiet pavements. Porous mixes should not be placed in
urban areas where the operating speed drops below 72 km/ h ( 45 mi/ h) since highly
porous mixes tend to clog under slow traffic.
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Section 3
Noise Reduction Survey
A survey questionnaire was developed to gather information from government and non-government
agencies regarding; a) current use and practices in the area of noise products,
materials, and technologies, b) current research on noise reduction methods, and c)
potential future use of noise reduction products, materials and/ or technologies. This
section of the report documents the methodology used to develop the survey questionnaire,
potential respondents targeted by the survey, and the execution of the survey. The survey
questionnaire results are discussed in Section 4.
3.1 Development of Questionnaire
The survey was designed to be short with no more than 10 questions. It was also designed
as an electronic survey to be distributed via email. Recipients had the option to mail back
the survey as a hard copy, if desired. The questions were arranged in the following order:
Leading Questions
Questions 1 through 4 were developed as leading questions that ask the potential
survey participant or “ respondent” about his/ her knowledge of different noise
products, materials, and technologies that were found in the literature review.
Budget
Question 5 asks the potential respondent to identify the amount ( or percentage) of
funds the their organization allocates for noise reduction projects on an annual basis.
Cost Benefit
Question 6 asks if a minimum reduction in decibels ( dB) is required before a noise
reduction project can be considered for implementation by the respondent’s organization.
Attribute
Question 7 asks how important certain attributes are when deciding to implement a
noise reduction project. Question 8 asks what attributes are important in deciding
against the implementation of a noise reduction measure or project?
Research
Question 9 asks whether the respondent’s organization was conducting any research on
the effectiveness of new noise reduction products, materials or technologies.
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Contact Information
In the event the research team had follow- up questions or needed clarification, each
respondent’s contact information was requested in Question 10.
3.2 List of Potential Respondents
One of the findings from the literature review was that the work of pavement noise
reduction has been primarily done by state transportation agencies, transportation related
organizations, universities, and consultants. This is not surprising, especially since the
nature of most road and highway work falls under the jurisdiction of state and local
governments. This narrows the list of potential respondents from a large sample population
to a very small one.
A list of potential survey respondents was created from state transportation organizations,
universities with transportation centers, professional associations, and vendors and sup-pliers
of noise reduction products. A list of 77 potential survey respondents was created.
3.3 Preliminary Noise Survey
A preliminary noise survey questionnaire was developed as a Microsoft Word document
and then converted to portable document format ( pdf). A cover letter and preliminary
survey questionnaire was e- mailed to 16 pre- survey respondents on February 24, 2006.
The 16 pre- survey respondents were selected from the list of 77 potential survey
respondents. A follow up response was sent to non- respondents about three weeks later.
The objective of the preliminary survey was to gain feedback/ input regarding the survey
form itself. Development of a preliminary survey prior to distribution of the full survey
allowed the study team to identify ambiguous questions, address formatting issues, and
correct possible deficiencies that may have been overlooked.
Each pre- survey respondent was asked to complete the attached preliminary survey
questionnaire and provide the study team with comments or other information regarding its
content and/ or structure. Another objective of the preliminary survey was to validate e-mail
addresses and other contact information for the pre- survey respondents.
If the pre- survey respondent had the ability to write to a pdf document, answers to the
preliminary survey questions could be made on the document, and emailed back to the
study team. If not, the pre- survey respondent was instructed to print a copy of the
preliminary survey, complete it and fax or mail it to the study team.
Two pre- survey respondents completed the preliminary pavement noise reduction survey
form and five pre- survey respondents provided comments. Each of the five pre- survey
respondents indicated that their organizations were not involved in noise reduction
research.
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3.4 Noise Reduction Survey
Minor changes ( mostly editorial or format related) were made to the preliminary pavement
noise survey questionnaire based on comments received. The final pavement noise
reduction survey was developed and e- mailed to the remaining 61 potential respondents as
well as the nine ( 9) pre- survey respondents who did not respond to the preliminary survey.
The first survey questionnaire was e- mailed on May 5, 2006 and a follow up mailing was
sent on May 16, 2006. Due to low response, a third e- mail was sent on June 28, 2006. All
non- respondents were called after the third mailing and encouraged to return the survey
questionnaire. If the individual was not in the office, a message was left on their voicemail.
Copies of the initial and follow- up cover letters and noise reduction survey questionnaire
are shown in Appendix 1.
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Section 4
Survey Results
This section provides a summary of the responses received from respondents who completed the
noise reduction survey questionnaire.
4.1 Overall Response Rate
Sixteen survey questionnaires were returned from the group of 77 potential respondents. This
represents a 20.9% overall response rate for the sample population. Of the 16 surveys that were
returned, two surveys were missing significant data. To not skew the data results, these two
surveys were eliminated from further analysis. Therefore, the effective sample size for the noise
reduction survey is 14 respondents.
4.2 Sample Validation
When a mail survey is conducted, there is no way to ensure that 100 percent of those surveyed
will respond to a questionnaire. For the Noise Reduction Survey, an e- mail survey was
considered to be the same as a regular postage mail survey. For some surveys, it is necessary to
conduct statistical tests to ensure that respondents are representative of the population, that there
is a minimum likelihood of response bias, and that the data are reliable. Statistical methods are
used to develop these answers. Due to the small sample population ( 77) and the even smaller
effective sample size ( 14), the data obtained from the Pavement Noise Reduction Survey is
statistically indeterminant. However, this in no way implies that the data obtained from the
survey is not useful to ADOT or other organizations.
This study utilizes the Convenient Survey methodology to assess respondents’ knowledge and
familiarity with products, materials, and technologies that are effective in reducing highway
noise. A Convenient Survey is very similar to a focus group that solicits opinions about a
particular product or service. It is less dependent on the sample size since one of its primary
purposes is to acquire knowledge and information related to a particular topic or subject matter.
Thus, the results from the 14 respondents in this study are comparable to what a targeted focus
group would provide.
4.3 Survey Results
Appendix 2 provides a detailed summary of the survey results.
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Section 5
Potential Growth of
Noise Reduction Measures
One of the findings of the literature review in Section 2 is the identification of several noise
reduction measures that are currently in use or undergoing research. Several European countries
have been engaged in pavement and other noise reduction measures associated with roadway
traffic since the 1980s or earlier. This comment was noted by several of the respondents in the
survey.
The results of the survey are documented in Section 4. Although limited, a few survey
respondents identified areas of future research and adoption by State DOTs with regard to traffic
noise products, materials, and technologies. In addition, these respondents indicated that a few
states such as California and Arizona have been at the forefront in researching noise reduction
methods. They noted that it is just recently that some of the other states have begun to consider
similar research activities in their transportation plans.
The objective of Task 4 of the Work Plan is to develop an assessment of the expected growth in
the acceptability and use of alternative noise reduction products, materials, and technologies.
This assessment is based on the findings from the literature review and the survey. Due to the
limited response from the survey, the assessment is largely based on findings from the literature
review.
5.1 Products
Noise wall barriers or sound walls have dominated this category for traffic noise reduction in the
United States, with approximately 165 million square feet of barriers as of 2004. Although this
category has shown growth over the years, continued growth of this traffic noise mitigation
measure is not expected in the future. The effectiveness of some sound walls has been called into
question, and is heavily tied to location and surrounding terrain.
Projected Growth: Replacement and repair of existing sound walls is required as part of routine
or ongoing maintenance. Growth in the variety of materials that can be used for sound walls will
continue, including the use of recyclable components. Those products that have been tested for
sound reduction with satisfactory results and are cost effective will continue to attract users.
Top coats and treatments for sound walls have been studied with mixed results. Further study in
this area is recommended for the potential to enhance the effectiveness of existing sound walls.
Use of modeling tools to enhance the design of existing and future noise walls is strongly
recommended.
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5.2 Materials
The noise reducing properties of OGFC, SMA, and HMA are well documented in the literature.
OGFC, which has been used in the warmer regions of Arizona, has a number of pavement noise
benefits. However, some of the shortcomings of this paving material are that it is not pervious to
rainwater, is not porous, and does not perform well in colder climates.
Projected Growth: The FHWA International Scanning Team ( IST) 13 provided a number of
recommendations for immediate implementation by transportation departments and other
organizations following their visit to five European countries in 2005 to review quiet pavement
practices. Two recommendations that were cited by the IST for immediate implementation are:
1. Two- layer Porous Mixes – early evaluation results in Europe indicate that TLPA
appears to have potential application on high- speed roadways and produces
exceptionally quiet pavements. Porous mixes should not be placed in urban areas
where the operating speed drops below 72 km/ hr ( 45 mi/ h) because highly porous
mixes tend to clog under slow traffic.
2. Reduce Aggregate Size – European practices show the aggregate sizes for quiet
surfacing mixes are between 0 and 4 mm ( 0.16 in) up to 0 and 10 mm ( 0.4 in).
Interestingly, most State DOTs use the Superpave aggregate gradings of 19 mm, 12.5
mm, or 9.5 mm ( 0.76, 0.5, or 0.38 in). Therefore, IST recommends a drop in routine
aggregate mix size to the next smallest gradation that could produce noise reductions
of 1 to 3 dB.
Since most of the quiet pavement work that has been completed to date in the U. S. has in
some way involved FHWA, those states that are just beginning to consider pavement
noise reduction projects are expected to seek guidance at the federal level and from other
more experienced State DOTs.
The benefits of NGOGFC were cited by TxDOT – good friction, lower noise, and in wet
weather: higher visibility, reduced splash and spray, reduced hydroplaning, and reduced
nighttime surface glare. ADOT and other State DOTs that are currently using OGFC
should also consider NGOGFC. NGOFC contains approximately 20% more asphalt by
volume than OGFC and has a minimum of 18% air voids. The void structure of
NGOGFC allows the mix to be more permeable and less likely to trap water. NGOGFC
appears to last twice as long as conventional OGFC. Although the problem of freezing in
colder climates has not been eliminated with NGOGFC, the pavement may hold up better
in cooler climates due to its more open graded mixture and thicker placement ( 1.5 to 2
inches vs. 1- inch for OGFC). NGOFC is 22.5% more expensive than OGFC. However,
the benefits and longevity may outweigh the additional costs.
The Netherlands has significant experience with double- layered porous asphalt construction. 11
Double- layer paving material consists of a bottom layer of coarse porous asphalt ( single- grained
gradation, aggregate size 11 to 16 mm ( 0.44 to 0.64 in) and a top layer of fine- graded porous
asphalt, aggregate size 4 to 8 mm ( 0.16 to 0.32 in)). Rubberized asphalt is used as the binder in
both layers. The double- layer porous mixture may also have applications for colder climates.
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Although the extent of testing and application are limited, two materials that deserve more
investigation for their noise reducing properties are Italgrip and RCI. Each product has been used
with PCC to reduce highway levels. KDOT placed 3 inches of asphalt over a 1 inch RCI layer
across an eight- mile stretch of I- 435. Noise reduction levels of 7 dB were reported. Italgrip is a
very thin surface treatment consisting of a two- part polymer resin placed on the pavement
surface and covered with a man- made aggregate of re- worked steel slag 3 to 4 mm ( 0.12 to 0.16
in) in size. In a cooperative effort with the Highway Innovative Technology Evaluation Center
( HITEC), several states with different climatic conditions will test and evaluate the Italgrip
System. When available, ADOT should review these tests to further evaluate the effectiveness of
this thin surface treatment.
5.3 Technologies
One of the results from the literature review is a list of potential texturing techniques that
that may be effective in reducing tire- pavement noise. Another finding is a growing field
of techniques that are being studied to impart texture to pavement surfaces. Prior to
making a decision on a pavement surface texturing treatment, the percentage of heavy
vehicles should be considered in determining overall effectiveness of surface treatments.
Projected Growth: Pavement texturing recommendations cited by the IST13 are:
1. Thin- textured Surfacings – use of thin- textured surfacings with small aggregate size
is recommended for urban or low- speed roadway sections. To achieve noise
reduction, texture should always be negative ( pavement depressions).
2. Diamond- grinding – investigate and optimize the use of diamond- grinding blade
configurations to enhance noise- reducing properties of existing concrete surfaces in
sensitive locations.
3. EAC – research the use of EAC for construction of new concrete pavements.
Traditionally, transverse tining has been the most common texture on high- speed roads
and highway pavements in the United States. Longitudinal tining has been gaining in
acceptability and use and exhibits lower noise characteristics. Pavement design of
longitudinal tining ( minimum of 25% siliceous sand) is important to improve long- term
effectiveness.
Diamond grinding has been traditionally used to rehabilitate existing pavement and to restore
smoothness with the unexpected outcome of a quieter pavement. As recommended by Cackler, 16
“ only when the texture geometry can be characterized along with the corresponding noise and
other pavement surface characteristics will the optimum ‘ whisper grind’ technique be fully
realized.”
The technique of negatively texturing pavements, the equivalent of making a depression in the
pavement, is being perfected. According to Cackler, to move into the low- noise Zone 1, the
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concrete pavement industry will have to embrace innovative solutions such as increasing
porosity, minimizing adverse texture wavelengths, or even modifying mechanical properties,
including stiffness. Successful products may include the use of pervious concrete, inclusions, and
polymers. Negative textured pavements are probably the only solution in Zone 1. Zone 1 is the
low noise level or “ innovation” zone, with on- board sound intensity ( OBSI) values at about 99 to
100 dBA and below range.
5.4 Other Measures
This report provides many examples of successful applications of traffic noise products,
materials, and technologies in the United States and other countries. However, noise or sound
reduction cannot be achieved by these measures alone. Effective land use planning is another
important component of successful reduction in highway noise. State DOTs should consider
encouraging local jurisdictions to enact noise ordinances and land use regulations to guide new,
noise- compatible development adjacent to major highways. 19
Another recommendation from IST is to update current noise policy and traffic noise models to
take advantage of the benefits of an integrated approach with other noise mitigation alternatives.
As reported at the InterNoise 2003 Conference, 21 transportation officials from The Netherlands
were developing several projects under the IPG that focus on an integrated approach - the use of
silent roads, improvement of tires and vehicles, optimization of barriers, knowledge management
and facilities and assessment methods – to achieve greater noise reduction. A similar approach is
strongly encouraged at the State DOT level.
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Section 6
Conclusions and Recommendations
This research study was undertaken to compile information on traffic noise reduction
products, materials, and technologies that are currently available, and if appropriate to
this transportation agency’s needs, to assess what could be implemented with reasonable
effort. A review of the literature was undertaken. The research quickly identified large
volumes of information on traffic noise reduction measures. Traffic noise is defined here
as sound from the roadway that is heard as a result of vehicle use.
The regulation of many sources of noise, such as engine noise, blowing horns, noise from
residential or commercial buildings, etc. is outside the jurisdiction of a state
transportation agency. Most of the focus of this study was traffic noise reduction
products such as sound walls and sound wall treatments, as well as pavement noise
materials and technologies.
The literature review and noise survey identified measures that are being used by U. S.
transportation organizations as well as international efforts. Some key findings from the
literature review show the following best practices:
• Traffic Noise Reduction Products – noise or sound walls dominate this
category and have been used for decades in the U. S. The effectiveness of
sound walls has at times been called into question. Better design parameters
are needed to ensure that noise is properly deflected away from receptors.
However, existing noise walls have to be maintained and sometimes replaced.
Findings from the literature revealed a variety of materials to choose from that
are both aesthetically attractive, and effective in reducing noise from highway
vehicle use. The cost of installing products will need to be evaluated on a case
by case basis with the vendor or for each applicable product.
• Traffic Noise Reduction Materials – The operating speed of the roadway
should be factored into the roadway design for quiet pavements. European
studies show that higher porous mixtures tend to clog under slower speeds
( less than 72 km/ hr, 45 mph).
• Two layer- porous mixes have been found to be effective in Europe and the
U. S. An important attribute for consideration in two layer- porous mix design
and placement is aggregate size. Most State DOTs use the Superpave
aggregate gradings of 19 mm, 12.5 mm, or 9.5 mm ( 0.76, 0.5, or 0.38 in).
Current recommendations are to drop the routine aggregate mix size to the
next smallest gradation, with an expectation of reducing noise levels 1 to 3 dB.
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• Pavement Noise Reduction Technologies - use of thin- textured surfacings
with a negative pavement depression are recommended for urban or low-speed
roadway sections. Diamond grinding enhances noise reduction on
concrete surfaces in sensitive locations.
• Other Pavement Noise Reduction Measures – looking forward, transportation
officials are encouraged to develop an integrated approach to roadway noise
reduction. Instead of relying on a single measure, the recommended strategy is
to develop the ability to model the effectiveness of a number of different
measures.
EAC and pervious concrete pavements have been identified as promising innovate
concrete solutions. These technologies require further study or specification development
before becoming part of paving practices in the United States.
Looking forward, a number of innovative traffic noise research programs are currently
underway, both in the United States and Europe. As an example, the Netherlands is
developing several silent pavement projects under their Noise Innovation Program. These
projects not only focus on pavement materials or texturing techniques, but also
improvement of tires and vehicles, knowledge management, and assessment methods.
The outcomes of these projects should be documented to determine if they are applicable
and cost effective for use on Arizona’s highways.
Many State DOTs’ noise reduction programs are in their infancy. Those states that have
established programs for noise reduction within the last decade ( including Arizona) will
be sought after for their expertise in the area, including pavement noise reduction.
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List of References
1. Manuel, John. 2005. “ Clamoring for Quiet; New Ways to Mitigate Noise”.
Environmental Health Perspectives 113( 1).
2. FHWA Noise team. 2001. Keeping the Noise Down: Highway Traffic Noise
Barriers. Washington D. C. Agency report.
3. Federal Highway Administration ( FHWA). 2006. Highway Traffic Noise in the
United States: Problems and Response. Agency Report.
http:// www. fhwa. dot. gov/ environment/ probresp. htm, viewed Oct. 02, 08.
4. www. acoustics. com, web definition. Viewed June 15, 2006
5. Butler, G. F. 1974. “ A note on improving the attenuation given by a noise
barrier”. Sound and Vibration, 32( 3) 367- 369.
6. Mongeau, Luc, J. Stuart Bolton, and Sanghoon Suh. 2003. Investigation of Novel
Acoustic Barrier Concepts Phase I: Concept Development and Preliminary
Evaluation. Final Report:. The Institute for Safe, Quiet, and Durable Highways,
Purdue University.
7. Same as reference # 6 above.
8. Same as reference # 6 above.
9. Rubber Pavements Association. 2000 ( Summer). Newsletter 2 ( 2),
http:// www. asphaltrubber. org/ RPA_ Newsletters/ summer2000/ page4. html Last
viewed July 14, 2008
10. Kandhal, P. S. 2004. “ Asphalt Pavements Mitigate Tire/ Pavement Noise”, Hot
Mix Asphalt Technology. March/ April Ed.
11. Venner Consulting and Parsons Brinckerhoff. 2004. Compendium of
Environmental Stewardship Practices, Procedures, and Policies for Highway
Construction and Maintenance. NCHRP Project Report 25- 25( 04).
12. Fults, Ken et. al. June 2005. Cold Weather Performance of New Generation
Open Graded Friction Courses. Austin, Texas. Project 04- 834. Presentation.
13. Federal Highway Administration. 2005. Quiet Pavement Systems in Europe.
International Technology Exchange Program, Report No. FHWA- PL- 05- 011
14. Kansas DOT. 2005. KDOT’s I- 435 Project Provides Good Road, Quiet
Alternative. Hot Mix Asphalt Technology Source
15. Kuemmel, David et al. 2000. Investigative Study of the Italgrip System: Noise
Analysis. Report Number WI/ SPR- 02- 00. Wisconsin Department of
Transportation.
16. Cackler, E. Thomas. July 2006. Evaluation of U. S. and European Concrete
Pavement Noise Reduction Methods. Iowa State University. National Concrete
Pavement Technology Center.
42
17. Meiarashi, Seishi. 1996. Porous Elastic Road Surface as an Urban Highway
Noise Measure. Tsukuba Ibaraki Japan. Public Works Research Institute.
18. Dutch/ Danish Delegation. 2006. Noise Reducing Pavements in Japan.
http:// www. vejdirektoratet. dk/ publikationer/ VInot031/ index. htm Study Tour
Report. Viewed July 14, 2008.
19. American Concrete Pavement Association. 2005. ACPA Concrete Pavement
Progress. 41 ( 7).
20. Marsella, Mark. December 1997. Reduction of Traffic Noise at the Source. New
Jersey Department of Transportation.
21. American Concrete Pavement Association. October 2006. “ Rules of Thumb on
Pavement Noise,” Concrete Research & Technology. 7.
22. Hoffman, Rob and Jasper van der Kooij. 2003. Results from the Dutch Noise
Innovation Program Road traffic ( IPG) and Roads to the Future Program
( WnT)”. 32nd International Congress and Exposition on Noise Control
Engineering. Netherlands.
23. Cable, James K. and James P. Fentress. 2004. Two- Lift Portland Cement Concrete
Pavements to Meet Public Needs. Final Report. Iowa State University.
24. Sandberg, Ulf. August 2005. Low Noise Road Surfaces, State- of- the- Art.
Presentation at EU Project Silenda Via ( SILVIA), International Seminar, Swedish
Road and Transportation Institute. Brussels, Belgium.
43
Appendix 1
Selected Noise Reduction Survey Documents
• Survey Cover Letters Page 45
• Survey Document Page 47
44
45
46
47
48
49
50
51
Appendix 2
Noise Reduction Survey Resposes
ADOT Transportation Research Center
Figure A2- 1: Noise Reduction Survey
Summary of Responses
1. How familiar are you with the following Sound Abatement Products, Materials or Technologies?
Don’t Not Somewhat Very Extremely
Know Familiar Familiar Familiar Familiar Familiar
Pavement Alternatives
- Dense grade asphalt 1 2 0 8 2 1
- Rubberized pavement 0 2 5 3 4 0
- Portland cement concrete 0 0 4 4 6 0
- Other 7 1 3 3 0 0
Traffic Noise Barriers
- Sound Absorbing Noise Walls 0 0 1 6 5 2
- Earth Mounds or Berms 0 0 0 7 5 2
- Other 8 3 1 1 1 0
Traffic Noise Barrier Treatment
& Coatings
- Crumb rubber 0 6 4 1 2 1
- Innovative noise barrier design 1 4 4 3 2 0
- Other 8 3 1 1 1 0
Receptor Controls
- Land Use Planning 0 0 8 1 3 2
- Window Treatments 0 4 7 2 1 0
- Other 8 4 0 2 0 0
2. How effective are the following Products, Materials, or Technologies in reducing
pavement and traffic noise?
Don’t Not Somewhat Very Extremely
Know Effective Effective Effective Effective Effective
Pavement Alternatives
- Dense grade asphalt 1 2 1 7 2 1
- Rubberized pavement 0 1 7 4 1 1
- Portland cement concrete 1 1 4 6 2 0
- Other 7 3 2 0 1 1
Traffic Noise Barriers
- Sound Absorbing Noise Walls 2 2 2 6 1 1
- Earth Mounds or Berms 1 1 3 4 1 4
- Other 8 3 2 0 1 0
52
Traffic Noise Barrier Treatments
& Coatings
- Crumb rubber 6 0 1 6 0 1
- Innovative noise barrier design 1 4 1 2 6 0
- Other 8 5 0 0 0 1
Receptor Controls
- Land Use Planning 1 0 6 3 1 3
- Window Treatments 1 3 7 3 0 0
- Other 2 6 4 0 1 1
3. If you are familiar with the following brands or products listed below, how would you
rank their effectiveness in reducing highway pavement noise?
Don’t Not Somewhat Very Extremely
Know Effective Effective Effective Effective Effective
Products
SoundSorb 8 0 0 4 0 0
Whisper Wall 10 0 1 1 0 0
Quilite Walls 11 0 1 0 0 0
Carsonite Sound Barrier System 8 0 1 2 1 0
Paraglas Sound Stop 9 0 0 3 0 0
AcoustaCrete 10 1 0 1 0 0
Crumb Rubber Coatings 9 0 1 2 0 0
Top Treatment ( for sound barriers) 11 0 1 0 0 0
NOISHIELD 12 0 0 0 0 0
Starkustic 12 0 0 0 0 0
Soundblox 10 0 1 1 0 0
Broad Band Sound Absorber 11 0 0 0 1 0
Perma Delta Sound Barrier 12 0 0 0 0 0
Coustiview 12 0 0 0 0 0
Materials
Porous Friction Course 2 0 3 4 2 2
Dense Graded Hot Mix Asphalt 2 1 7 2 1 0
Stone- Matrix Asphalt Concrete 5 1 2 3 2 0
Street Absorbing Membrane
Interlayer 10 0 0 2 0 0
Portland Cement Concrete 2 4 3 3 1 0
Technologies
Hot Mix Asphalt 3 2 5 0 2 1
Surface Texturing 3 0 3 4 2 1
Bonding Road 11 0 2 0 0 0
Modieslab 12 0 0 1 0 0
53
4. Do you know other noise reduction Products, Materials, or Technologies not listed above?
Please list their names below.
5. On the average, what percentage of your highway budget is allocated for noise reduction
measures in highway projects? 10 respondents reported a range of 1 to 5% ( average of 2.1%) of their
highway budget is allocated for noise reduction measures.
6. Does your Agency require a “ noise benefit factor” before implementing sound reduction
measures? Example, a noise benefit of three ( 3) decibels is required before implementing sound
reduction measures in a highway project.
10 respondents said “ Yes”, 1 respondent said “ No”, and 2 respondents said it “ Varies by Project”
7. How important are the following in considering and implementing sound abatement measures in
your highway projects:
Not Somewhat Very Extremely
Important Important Important Important Important
Cost Effectiveness 0 0 0 11 3
Technology Maturity 0 1 6 4 3
Durability 0 0 2 6 6
Low Cost and Convenience
in Installation 0 5 3 5 1
Low Cost, Convenience
in Maintenance & Repair 0 4 3 5 2
Aesthetics 0 0 9 5 0
8. When it come to your agency NOT using hot mix asphalt and other Technologies to abate traffic
noise, how important are:
Not Somewhat Very Extremely
Important Important Important Important Important
Cost Effectiveness 1 0 4 5 2
Technology Maturity 1 1 4 4 2
Durability 1 0 2 8 1
Low Cost and Convenience
in Installation 1 3 2 5 1
Low Cost and Convenience
in Maintenance & Repair 1 2 4 4 1
Federal Guidelines ( not QPPP approved ) 4 0 4 2 1
More Research and Testing Needed 0 2 5 2 3
Products Materials Technologies
Other 1 Durisol Precast Concrete Planting buffers
Evergreen Wall Recycled plastic
Nova Chip
Other 2 Hoover Wall ( wood) No response Site design
Other 3 No response No response No response
54
9. Is your Agency currently conducting research or studying the effectiveness of new noise
reduction Products, Materials or Technologies?
13 respondents said: No = 5, Yes = 8, No Response = 1
If yes, list:
Products Materials Technologies
Item 1: Durisol Sound Absorptive - 1 Rubberized pavement - 1 Texturing - 2
Nova Chip - 1 OBSI* - 1
Item 2:
Item 3: Pavement types - 1
* OBSI – On board sound intensity ( for noise measurement)
10. May we contact you in the future, concerning noise reduction, Products, Materials or
Technologies?
Name of Organization: _____________________________________
Contact Person: _______________________________________
Phone Number: _______________________________________
Email Address: _______________________________________
Thank you very much for your time and consideration in assisting us with this project.
55
A discussion of the Pavement Noise Reduction Survey is presented in this appendix. A
summary of the responses to the Pavement Noise Survey questionnaire is provided in
Figure A4- 1.
A. 2.1 Knowledge of Products, Materials, or Technology
Question 1: How familiar are you with the following Sound Abatement Products,
Materials or Technologies?
Most of the respondents reported being somewhat to extremely familiar with each
pavement noise reduction product, material or technology listed under Question 1.
The most responses were reported for:
o Pavement Alternatives: Dense grade asphalt – 8 Familiar ( 57.1%)
o Traffic Noise Barriers: Earth mounds or berms – 7 Familiar ( 50.0%)
o Receptor Controls: Land use planning – 8 Somewhat Familiar ( 57.1%)
o Receptor Controls: Window treatments – 7 Somewhat Familiar ( 57.1%)
No additional responses were provided for “ Other” pavement alternatives, traffic
noise barriers, traffic noise barrier treatment and coatings, or receptor controls.
Question 2: How effective are the following Products, Materials, or Technologies in
reducing pavement and traffic noise?
Respondents were asked to identify the effectiveness of each noise reducing
product, material, or technologies listed:
o Pavement Alterations:
􀂃 Dense grade asphalt – 7 Effective ( 50.0%)
􀂃 Rubberized pavement – 7 Somewhat Effective ( 50%)
o Traffic Noise Barriers: Sound absorbing noise walls – 6 Effective ( 42.9%)
Additional Comments: TxDOT has only used absorptive treatment on
an experimental basis. The research work focused on construction
techniques rather than acoustical properties. TxDOT has rarely
considered/ used earth mounds/ berms due to insufficient right- of- way
for construction.
o Traffic Noise Barrier Treatment and Coatings:
􀂃 Crumb rubber – 6 Don’t Know ( 42.9%) and 6 Not Effective ( 42.9%),
o Receptor Controls: Window Treatments – 7 Somewhat Effective ( 50%)
Additional Comments: TxDOT has developed a comprehensive
presentation on “ Noise Compatible Land Use Planning.”
No additional responses were provided for “ Other” pavement alternatives, traffic noise
barriers, traffic noise barrier treatments and coatings, or receptor controls.
56
Question 3: If you are familiar with the following brands or products listed below, how
would you rank their effectiveness in reducing highway pavement noise?
A list of some of the pavement noise reducing products, materials or technologies
identified in the literature review were included in this question. Not surprisingly, most
respondents checked “ Don’t Know” for the list of products. Four ( 28.6%) of the
respondents indicated that the noise barrier product, SoundSorb, is somewhat Effective.
For the Materials listed, 7 ( 50%) identified dense graded hot mix asphalt ( DGAC) as
“ Somewhat Effective” at reducing pavement noise, and 10 respondents ( 71.4%) chose
“ Don’t Know” when asked about the effectiveness of a street absorbing membrane
interlayer.
Although HMA is considered a paving material, it is also included as a technology due to
the process used to place the pavement. Five ( 5) respondents identified HMA as
“ Somewhat Effective” as a pavement noise reduction technology.
Question 4: Do you know other noise reduction Products, Materials, or Technologies
not listed above? Please list their names below.
When asked about the respondent’s knowledge of other pavement noise reduction
products, materials, or technologies that were not listed in Questions 1 to 3, only
three of 14 respondents provided additional information. Some items provided by
the respondents are improperly categorized, e. g. planting buffers and site design
are not technologies, however, these responses are included in information
reported in the literature review
57
Question 5: On average, what percentage of your highway budget is allocated for noise
reduction measures in highway projects?
Eleven ( 78.6%) of the 14 respondents reported that 1 to 5% ( average of 2.1% for survey)
of their department’s budget is allocated for noise reduction activities ( see Figure A4- 2